Scientific Landmarks in the Study of H.M.

 

This diagram shows a timeline of the historical scientific landmarks that researchers have discovered while studying HM (Corkin, 2002).

 

Click on Image to Enlarge.

 

H.M., His Memory and His Contribution to Neuropsychology

 

HM, who is also known as Henry M. was born in Connecticut in 1920.  At the age of seven, HM was in a bicycling accident and suffered a head injury.  After this accident, HM developed epilepsy and experienced many partial seizures and after age 16 suffered several total brain seizures.  In 1953, he was referred to William Scoville, a surgeon in Hartford, for treatment (Corkin, 2002).

 

In Hartford, Scoville examined HM’s brain extensively to determine the cause of his epileptic seizures.  Scoville finally localized the seizures to HM’s medial temporal lobe.  Dr. Scoville suggested a removal of the medial temporal lobes to help treat the seizures (Corkin, 2002).  On September 1^st 1953, Dr. Scoville removed parts of HM’s medial temporal lobe on both sides of the brain.  HM ended up losing two-thirds of his hippocampus region, and amygdala.  The remaining parts of the hippocampus appear to be non-functioning in HM, as the parts have atrophied and show no functional response (MacKay, 1998).

 

Although the surgery helped cure HM’s seizure problems, it rendered him an anterograde amnesiac, which means that he is unable to commit new memories from short term memory to long term memory (Corkin, 2002).  HM also appears to suffer from a mild case of retrograde amnesia, as he is unable to remember the 3-4 days prior to his surgery or specific life events which occurred up to 11 years before the surgery.  Many studies have been conducted to observe the extent of memory damage in HM.  Scientists believe that HM is unable to make any new semantic memories, however, other scientist would debate this issue (Milner, 1968).  A study by Dr. Scoville showed that HM has the ability to form long term procedural memories.  HM was asked to perform a mirror drawing test, and as the study progressed, HM began to show a learning effect, even though HM could not recollect ever having performed the task (Corkin, 2002).  More tests were completed and it was also found that HM showed a learning effect for both tapping tasks and pursuit rotor tasks.  In one specific task, the Tower of Hanoi, HM even showed problem-solving abilities.  HM’s performance on these different tasks has given researchers great insight into the ideas of explicit and implicit memory (Milner, 1968).

 

It is most unfortunate that HM suffered a brain injury that has forever impaired his memory. However, due to his ill-fated bicycling accident, HM has provided many researchers and scientists with great insight into different areas of neuropsychology.   His condition and impairment have helped scientists establish a broader picture of what is a normal functioning brain. Because of HM, scientists have been able to map areas of the brain that are responsible for specific functions and memory systems (Milner, 1968).  HM has allowed scientists to gain more insight into amnesia, as well as memory formation within the brain.  In the last 50 years, HM has been at the center of information surrounding short term memory, long term memory, procedural memory, spatial memory and brain function.  There have been over 100 investigations involving HM, as many researchers believe that this is a once in a lifetime opportunity to gain valuable neuropsychology insight (Corkin, 2002).  HM’s dedication to research has many scientists feeling that they are in his debt. 

 

If you are interested in finding out more about HM, author Philip J. Hilts has written a book entitled Memory’s Ghost, which details the author’s personal meetings with HM, as well as providing further discussion about HM’s condition and contributions to science. 

 

Currently, HM is living in a nursing home in Hartford and makes occasional trips to MIT for memory testing.  He lives a peaceful and happy life and is said to have a sense of humour about his condition (Corkin, 2002).

Contributions to Memory Research

 

What can be accomplished without a hippocampus?

 
Through studies performed on K.C., it has been established that even without a functional hippocampus, priming can occur for pre-existing and self-generated novel word associates, it is modality specific, and it can last on the order of 30 minutes in some cases and up to 1 year in others. It has been shown that at least some types of spatial memory, including representing allocentric cognitive maps, can be independent of the hippocampus over time. The same extra-hippocampal regions implicated in various dissociable aspects of spatial memory on the basis of earlier case studies (Aguirre & D’Esposito, 1999) are engaged by K.C. and healthy controls.
 
The separation of memory and amnesia
 
Research on K.C. has demonstrated that it is not necessarily the case that episodic and semantic memory follows the same trajectory of impairment and preservation.  K.C.’s amnesia affects at least two dimensions of memory: the first is related to the quality or type of to-be-remembered information as just mentioned, and the second relates to the way in which information is processed in memory.  Similar to H.M., K.C. has difficulties in learning and retaining any consciously apprehended information encountered after the onset of his brain damage.  Any facts that K.C. has learned about the world and of himself that has occurred over the years is accomplished under incidental or highly constrained learning conditions, with the resulting representations fragmentary and detached from existing knowledge. From the completed research, it has been stated that K.C. may be said to have global anterograde amnesia that coincides with retrograde episodic amnesia. It is remarkable that despite K.C.’s extensive brain damage, his cognitive abilities are generally well preserved.

Experimental Investigations

 

Studies of new learning

 

K.C. is much different from H.M. because of his extensive brain damage at many different sites/areas, which has caused him both retrograde and anterograde amnesia.

 

In a study employing semantic memory (general facts), K.C. was able to demonstrate learning new semantic knowledge by remembering a target word (Parakeet) when cued with a definition (talkative featherbrain). The fact that K.C. was able to learn semantic knowledge is contrary to the generalizations found in literature that claim persons with amnesia cannot learn new factual information.  The study revealed that learning semantic knowledge depends on both the amnesic patient and the conditions under which learning occurs.  Because he is unable to associate meaning to this knowledge, K.C.’s ability to learn semantic knowledge, reminds us of the nature of his injury and confirms that his learned knowledge is simply non-relational semantic learning.

 

 

K.C.’s retrograde memory

 

K.C. has remote memory loss for factual information that is minimal in duration, and he also has memory loss for personal episodes that encompass his entire past.  Furthermore, K.C. demonstrates a severe impairment of autobiographical memory that covers his whole life.  This impairment of autobiographical memory includes response to actual visits to houses that he had lived in and schools that he had attended (Tulving et al., 1988) and to family photographs of past and more recent events (Westmacott, Leach, Freedman, and Moscovitch, 2001).

 

K.C. is unable to correlate any of the family photographs of past and more recent events to other life experiences.  After K.C. views a photograph, he is unable to elaborate beyond his instantaneous perception of the photograph, as though it was the first time he encountered the events being portrayed.  He also has a limited ability to identify people in a photograph; however he is able to recognize people encountered in his childhood, adolescence, and early adulthood with much greater ease than those he met for the first time in the years after his accident (Westmacott et al., 2001).

 

The results of a specific experiment performed by Tulving et al. (1988) illustrate that repeated visual exposure of knowledge unique to the job that K.C. held during the 3 years before his accident allowed for the progressive improvement of such expert knowledge, including the names of co-workers and familiarity with work-related technical terms and equipment presented in photographs.

Retrograde spatial memory

 

K.C. is able to easily negotiate his way in a neighbourhood familiar from youth, which represents that spatial memories acquired long ago might not be affected by hippocampal damage (Beatty et al., 1987; Milner et al., 1968; Zola-Morgan et al., 1986).  He is also able to perform normally on more structured mental navigation tests of his neighbourhood, including estimation of direction and selecting the most direct route between locations while avoiding an obstructed street.  K.C. also has the ability to perform normally on spatial tasks including accurate placement of streets in relation to one another in a sketch map, recognition and identification of neighbourhood landmarks, estimating absolute and relative distances between landmarks, sequencing randomly ordered landmarks along a route, and locating gross geographical features on outline maps of the world.  The following figure represents the sketch maps of a neighbourhood learned long ago drawn in 1986 and 1999 by K.C. (top row) and by a friend who moved away at the time of K.C.’s brain injury (bottom row).

 

                                                                                  ((Rosenbaum et al., 2005)

 

However, K.C.’s ability to perform normally on spatial tasks contrasts with his inability to acquire spatial information in a new environment.  He is unable to recall the spatial locations of common objects on a board following a short delay (Smith & Milner, 1981), a floor plan of a library in which he has worked since 1997, and a simple route after receiving extensive training.  These results were evident because this information is complex and associative in nature, requiring the hippocampus for integration.  K.C. also has difficulty in identifying specific features on outline maps of Canada and Ontario and he has difficulty sketching a map with respect to landmark inclusions, which suggests that his remote spatial memory does not appear to be completely intact (Rosenbaum et al., 2000).  K.C.’s loss of memory for topographical details and environmental features resembles the loss of contextually rich and detailed memories of autobiographical episodes.

 

The parts of K.C.’s brain that support spared memory

 

It is believed that the little remains of K.C.’s hippocampus may be functional enough to support mental representations of landmark appearance and location along routes, as well as distance and direction calculations, if this information was well established prior to his injury.  The extra-hippocampal structures on the right side of K.C.’s brain are engaged in a way that is consistent with the pre-eminent processing demands of each task.  When K.C. is required to imagine movement along routes and judge the direction of vectors between landmarks, regions in the posterior cingulate and posterior parietal cortex are consistently and uniquely active.

 

K.C. differs from control subjects in which no hippocampal activity is evident when he performs tasks successfully, even though he has part of his hippocampus still remaining.  The lack of hippocampal activity provides evidence that allocentric spatial representations of familiar environments are not dependent on the hippocampus.

 

Neocortical accounts of K.C.’s impaired remote memory for personal and spatial details

 

Although K.C. has a perceptual deficit in colour vision, he has shown preserved imagery for shapes of letters and animal body parts, the relative size of objects, and the colour of objects (Farah, Hammond, Levine, & Calvanio, 1988).  He has an intact imagery on real-world topographical tasks, which is evident in his intact imagery for spatial relations of hands on a clock (Paivio, 1978) and of a supposed route along the perimeter of block letters (Brooks, 1968).  However, K.C. is unable to produce a single personal story from any time in his life, however remote the episode.  Even with supplementary retrieval support in the form of specific cueing, K.C.’s performance continued to remain well below control levels.  The following figure portrays the total number of episodic details given by K.C. and demographically matched control participants for all life events during recall (left) and after specific probing (right).

 

 

((((Rosenbaum et al., 2005)

 

The events that K.C. is able to generate with fairly rigorous verbal prompting were still lacking the richness in episodic detail typical of personal incidents recalled by control participants.  However, progressive priming helped K.C to restore some of his remote personal semantic memories (Tulving et al., 1988).  The studies performed on K.C. assist in discounting impaired visual imagery and deficits in effortful, organizational retrieval as explanations for his impaired remote autobiographical memory.  There is evidence that autobiographical memory relies on the amygdala and parahippocampal gyrus, which are structurally compromised in K.C. (Maguire et al., 2001).

Neurological Status and Neuropsychological Profile

 

Detailed neurological studies have established that K.C. cannot identify or discriminate smells due to bilateral inosmia, a term defined as ‘no sense of smell, due to loss of the sense of smell or failure to develop it’ (Rosenbaum et al., 2005; Medicine Net Inc., 2008). 

 

He also suffers from glaucoma in the left eye, which causes progressive visual loss. Aside from these difficulties, along with decreased dexterity in the right hand and wide-stepped gait, K.C. displays normal neurological performance (Rosenbaum et al., 2005).

 

 

General Intellectual Cognitive Function

 

Apart from the domain of episodic memory, K.C.’s intellectual and cognitive function is well preserved. He displays normal language functional skills and his working memory is intact, as proven by tests where he is required to remember sequences of digits in both forward and reverse directions (Rosenbaum et al., 2005).

 

Anterograde Memory Function

 

K.C. displays severe anterograde memory impairment, meaning that he has difficulty with new learning and suffers greatly from an inability to retain new information. This has been confirmed many times by a series of memory tests. He is unable to recall words and faces regardless of how the material is presented and how he is required to recall information (e.g. verbal, non-verbal, free recall, or yes-no recognition). On the rare occasion he does retain information; however, it is lost after 20-30minutes (Rosenbaum et al., 2005).

 

 

Retrograde Memory Function

 

K.C. also displays severe retrograde memory impairment, meaning that he has great difficulty recalling information prior to his accident in 1981.  Testing his autobiographical incidents investigated his ability to recall unique episodes, such as the passing of a loved one or marriage of a close friend or relative.  Testing facts pertaining to one’s past, known as personal semantic information, revealed similar results.  K.C. “could not produce any single episode from his past that was distinct in time and place” (Rosenbaum et al., 2005).

 

Magnetic Resonance Imaging (MRI) of Brain Pathologies

 

Below is a series of MRIs of K.C.’s brain.  The images show the extent of the physical damage that resulted from his traumatic motorcycle accident.  The damage has ultimately led to his current psychological and cognitive functional deficits. Dark areas indicate damaged tissue.

Images of K.C.’s brain. The right hemisphere is shown on the left side of the images. The left hemisphere is affected to a greater extent than the right (Rosenbaum et al., 2005).

 

 

Images of K.C.’s brain, proceeding from right to left, as viewed from the right side (right sagittal view) of his head (Rosenbaum et al., 2005).

 

 

Below is an MRI scan showing minimal damage to the medial temporal lobe caused by atrophy (tissue loss). Dense matter is indicative of intact, functioning tissue (Barber et al., 1999).

 

 

 The series of MRI scans below show the extent of K.C.’s medial temporal lobe damage (tissue atrophy). Damage is clearly evident in both the right and left medial temporal lobes, as indicated by the white arrow pointing out the dark areas.

 

Images in axial (top), coronal (middle) and sagittal (bottom) views indicate the extent of damage in K.C.’s medial temporal lobe (dark signal areas) (Rosenbaum et al., 2005).

 

Implication of physical brain damage on cognitive functional ability

 

Damages to certain structures in the left hemispheres account for K.C.’s difficulty in perception of colour and face matching (recognition).  Damage to the posterior part of his brain is associated with his autobiographical memory loss—unique episodic memories—by affecting his visual imagery.  Damage to the frontal portions of his brain account for K.C.’s difficulty with phonemic fluency, that is, his ability to pronounce similar phoneme across many words (e.g. pronouncing the ‘t’ sound in tip, stand, and water) (Rosenbaum et al., 2005). The damage to K.C.’s medial temporal lobes (Figure above), is associated with his severe deficiency with new learning and memory.

Case History

 

K.C. is a right handed male with 16 years of formal education.  He was born in 1951 and raised in a suburb of Toronto, Ontario, Canada.

 

He suffered two head injuries during his adolescence and young adulthood with neither contributing to a change in cognitive functioning.  But in 1981, at the age of 30, a motorcycle accident resulted in brain trauma and left him with severe amnesia, along with many other cognitive function deficits.  He was discharged from the hospital in 1982 after a stint of long-term rehabilitation.  Even after rehabilitation, K.C. was unable to remember new information.  He could not remember events associated with breaking his knee and he displayed a similar horrified reaction when repeatedly told about September 11^th, 2001.  MRIs (magnetic resonance imaging) of his brain revealed severe damage to the medial temporal lobes – an area crucial in cognitive function, particularly in memory.

 

A Day in the Life…

 

K.C. is unable to recall meaningful personal experiences that he shares with close family and friends. His personality has also changed from a “thrill-seeking character…into one that is soft-spoken and tranquil” (Rosenbaum et al., 2005).

 

Here is a typical day in the life of K.C.:

 

“On most days, his mother wakes him before 7:30 h and 8:00h in the morning for breakfast. After finishing his meal, a note on the microwave door tells him to return upstairs for his daily exercise routine on a treadmill and stationary bicycle. He then dresses and grooms himself in preparation for one of his scheduled half-day excursions, which alternate between volunteering at a local library and participating in such activities as playing pool, swimming, and bowling with a small group of other head-injured people whom he again sees on Friday nights for dinner and a movie. Weekends in the summer and autumn are spent at the family cottage, as they were before his injury, and in the winter and spring at home visiting with family and friends. When nothing specific is planned, K.C. will sit down to play the organ, but he most enjoys playing card games on the computer (particularly Bridge and Solitaire) with the television on in the background (his favourite shows include “Mash” reruns and “The Price is Right”). He then eats dinner with his family, watches television and retires on his own at 11:00pm.”

(Rosenbaum et al., 2005)

 

Interestingly he is able to do the following, which may lead one to believe that he does not suffer complete loss of episodic memory function:

 

“Retention of the many skills and semantic facts learned in pre-accident years enables K.C. to locate without difficulty cereal and eating utensils in the kitchen, to know that the eight-ball is the last to sink in a game of pool, and to explain the difference between a strike and spare in bowling, and between the front crawl and breast stroke. He can describe the layout of his house and summer cottage, and the shortest route between them, without any recollection of a single event that occurred at either of these places. He expects a new ‘trick’ after four cards are placed in the centre of the Bridge table and anticipates Bob Barker on the “Price is Right” asking contestants to ‘spin the wheel,’ though he cannot foresee what he himself will do when the card game or television show is over. Like many individuals suffering from amnesia, he is also able to learn new information or skills normally, such as sorting books according to the Dewey decimal system in his library job, even though he is unable to recall explicitly the circumstances of this anterograde learning, indicating preserved implicit memory.”

(Rosenbaum et al., 2005)

K.C.’s Brain Pathology

 

As mentioned, K.C. suffers from two types of amnesia; Anterograde Amnesia and Retrograde Amnesia.

 

What is Amnesia?

 

Amnesia refers to a loss of memory for recalling facts, events, information and experiences, usually resulting from damage to the parts of the brain which control memory processing and learning (MayoClinic, 2008).  Amnestic syndrome prevents the learning of new information, as well as the formation of new memories and may even inhibit recall of past experiences and information (MayoClinic, 2008).This type of memory loss cannot be explained by attention, perception, language, reasoning or motivational problems. 

 

Types of Amnesia

 

There are three main types of amnesia; Anterograde Amnesia, Retrograde Amnesia and Transient Global Amnesia.

 

Anterograde Amnesia	Results in an impaired ability to learn new information following the onset of amnesia
Retrograde Amnesia	Results in an impaired ability to recall previously familiar information  and events that occurred prior to the onset of amnesia
Transient Global Amnesia	A temporary episode of memory loss

 

 

Causes

 

Amnesia is often the result of damage to brain structures that form the limbic system, which include the hypothalamus, hippocampus, amygdale, and cingulate gyrus of the cerebral cortex (Kalat, 2007).  The limbic system is particularly important for motivation, emotion and memory (MayoClinic, 2008).

 

Potential causes of brain damage/amnesia are:

• Stroke
• Brain Inflammation
• Lack of oxygen in the brain
• Subarahnoid Hemorrhage or bleeding between the skull and brain
• Wernicke-Korsakoff Syndrom, which results from long-term alcohol abuse leading to thiamine (Vitamin B-1) deficiency
• Brain Tumors
• Certain types of Seizure Disorders

 

There are currently no medications available to treat most types of amnestic syndrome (MayoClinic, 2008). 

 

As amnesia has a large impact on an individual’s ability to participate in typical daily activities and greatly decreases their quality of life, it is important to prevent amnesia whenever possible.  Because the main cause of amnesia is brain injury, it is important to minimize opportunity for brain damage to occur.  Avoiding excessive alcohol use, always wearing a helmet when cycling and a seat belt when in a vehicle and  ensuring any brain injury or infection is treated quickly will aid in reducing the chance of brain injury and therefore decrease the likelihood of developing amnesia (MayoClinic, 2007).

Sagittal Section Through the Brain

Cerebral cortex—often called the cortex or "the brain", the cerebral cortex is responsible for all higher thought processes. It manages and integrates information from all of our sensory organs, initiates movement and more complex actions, controls emotions, stores our memories, and gives us the ability to plan and think abstractly. 

The cortex is composed of neuron-dense "gray matter," and consists of the outer layer of the cerebrum. To fit the 230 to 465 square inches of valuable gray matter into our relatively small cranium, the cortex is pleated into folds (gyri) and grooves (sulci). The largest of these folds and grooves serve as dividers, separating the brain into two distinct hemispheres, each with four lobes.

(Adapted from PMI Memoryzine, 2008)

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Cingulate Gyrus—important in emotional functions.

(Martin, 2003)

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Frontal lobe—the foremost lobe in each of the two hemispheres of the brain that are responsible for executive control or supervision of cognition, language, associative processes including learning and memory, and motor coordination. Damage to this lobe of the brain can be devastating, and may result in paralysis, inability to plan sequences of complex movements, loss of spontaneity and flexibility of thought, problems focusing attention, mood changes and social interaction difficulties, and even the inability to speak or to understand language.

Some of the major substructures comprising the frontal lobe include:

• Precentral gyrus: the brain's motor center, which is directly connected to the somatosensory inputs in the parietal lobe and is responsible for processing and initiating all motor functions.
  
• Broca's area: located on the left side of the frontal lobe, this processes language by controlling the mouth, lips, and larynx (together responsible for the production of speech).

The majority of the frontal lobe is dedicated to what are called associative areas —areas of the brain from which we receive our ability to think creatively, problem solve, make judgments and reflect upon events.

(Adapted from PMI Memoryzine, 2008)

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Corpus Collosum—is a band of nerve fibers that connect the left and right hemispheres and transmits information between the hemispheres.

(Adapted from PMI Memoryzine, 2008)

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Ventricles – labyrinth of fluid-filled cavities that serve various supportive functions.

(Martin, 2003)

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Nucleus Accumbens – component of the striatum located ventrally and medially; a key structure in drug addiction.

(Martin, 2003)

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Hypothalamus—weighing only 4 grams and located beneath the thalamus at the base of the brain, this structure guides the autonomic nervous system's regulation of the function of internal organs, controls the endocrine system's release of hormones, and fuels basic biological drives including sex, hunger, thirst, sleep, and rudimentary emotional responses like pleasure and fear. It also plays a role in regulating body temperature, and helps coordinate the activity of the pituitary gland and the brain stem.

(Adapted from PMI Memoryzine, 2008)

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Pituitary gland—controls bone and muscle growth, the proper formation of reproductive structures, sexual maturation, and sexual and reproductive function. Its close collaboration with the hypothalamus means it also plays a key role in the regulation of basic bodily functions and biological drives.  It also regulates the hormonal secretions of many other glands throughout the body.

(Adapted from PMI Memoryzine, 2008)

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Pons—connects the two hemispheres of the cerebellum through its network of large nerve fiber bundles, and can be identified as a bulge directly in front of the cerebellum on the brainstem. The pons contains nuclei that deliver messages about movement and location for many parts of the body, back and forth between the cerebral cortex and medulla oblongata, and plays a role in establishing regular sleep, breathing and tasting functions.

(Adapted from PMI Memoryzine, 2008)

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Medulla oblongata—a primitive portion of the brainstem or hindbrain that controls basic life functions such as respiration, blood pressure, heartbeat, and muscle tone.

(Adapted from PMI Memoryzine, 2008)

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Spinal cord—participates in processing both sensory and motor information.  The spinal cord carries sensory information from the limbs, trunk, and many internal organs to the brain, as well as controlling body movements directly and regulating internal organ function.  

(Martin, 2003)

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Parietal lobe—this lobe gives us our sense of touch, the ability to understand form through touch and our recognition of stimuli from our own body’s pain, temperature, pressure, etc. It also aids in some speech and visual functions.

(Adapted from PMI Memoryzine, 2008)

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Thalamus—this lower section of the forebrain acts as the primary control center. It processes information coming from all the sensory pathways (except smell) before relaying it up to the cortex. It filters and determines which stimuli actually reach our consciousness, and which can be dismissed without cerebral input.  The thalamus is also responsible for sending out motor signal responses to the proper cortical areas.

(Adapted from PMI Memoryzine, 2008)

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Occipital lobe—a lobe dedicated almost entirely to managing vision and its associated functions. It receives and processes all visual stimuli delivered by the optic nerves and via the thalamus, and relays the processed information back through the midbrain, inferior temporal lobe, association areas of the parietal lobe, and the frontal lobe. A lesion in the visual cortex can produce a wide range of symptoms, from not being able to see in your peripheral field of view, to complete blindness.

(Adapted from PMI Memoryzine, 2008)

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Colliculi – two pairs of bumps—superior colliculi and inferior colliculi—located on the dorsal surface of the mid-brain.  The superior colliculi play an important roll in controlling eye movements and the inferior colliculi involved in the processing of sounds.

(Martin, 2003)

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Midbrain—houses a number of relay stations that transmit signals from the spinal nerves and hindbrain to the cerebral cortex. The midbrain is also responsible for sensory motor integration which controls the eye's reflex action and initiates primitive reflexes in response to pain, temperature, movement, and touch.

(Adapted from PMI Memoryzine, 2008)

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Cerebellum—bulb-like structure composed of two small hemispheres that regulate muscular coordination, voluntary movement, and balance. It also gives us our sense of our own bodies and where they are located in space.  Some theories suggest that the cerebellum retains rudimentary memory capacity for reflexes and sequences of motor activity—such as those required to ride a bicycle again after years have gone by since the last time one did. The cerebellum is connected to the brain stem via three bundles of nerve fibers called peduncles.

(Adapted from PMI Memoryzine, 2008)

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Dorsal (Top) View of the Limbic System

 

 (Kalat, 2007)

Cingulate Gyrus—important in emotional functions.

(Martin, 2003)

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Thalamus—this lower section of the forebrain acts as the primary control center. It processes information coming from all the sensory pathways (except smell) before relaying it up to the cortex. It filters and determines which stimuli actually reach our consciousness, and which can be dismissed without cerebral input.  The thalamus is also responsible for sending out motor signal responses to the proper cortical areas.

(Adapted from PMI Memoryzine, 2008)

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Hypothalamus—weighing only 4 grams and located beneath the thalamus at the base of the brain, this structure guides the autonomic nervous system's regulation of the function of internal organs, controls the endocrine system's release of hormones, and fuels basic biological drives including sex, hunger, thirst, sleep, and rudimentary emotional responses like pleasure and fear. It also plays a role in regulating body temperature, and helps coordinate the activity of the pituitary gland and the brain stem.

(Adapted from PMI Memoryzine, 2008)

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Mamillary Bodies—structures located in the diencephalon involved in learning.

(Adapted from PMI Memoryzine, 2008)

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Hippocampus—is a vital stakeholder in the formation and retrieval of memories.

(Adapted from PMI Memoryzine, 2008)

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Amygdala—lies deep within the cerebrum and is responsible for basic social behaviours and sex drive.  It is part of the limbic system.

(Adapted from PMI Memoryzine, 2008)

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Olfactory Bulb—the olfactory (smell) sensory organ.

(Martin, 2003)

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Right Side View of the Brain

http://health.allrefer.com/health/cranial-mri-lobes-of-the-brain.html

Frontal lobe—the foremost lobe in each of the two hemispheres of the brain that are responsible for executive control or supervision of cognition, language, associative processes including learning and memory, and motor coordination. Damage to this lobe of the brain can be devastating, and may result in paralysis, inability to plan sequences of complex movements, loss of spontaneity and flexibility of thought, problems focusing attention, mood changes and social interaction difficulties, and even the inability to speak or to understand language.

Some of the major substructures comprising the frontal lobe include:

• Precentral gyrus: the brain's motor center, which is directly connected to the somatosensory inputs in the parietal lobe and is responsible for processing and initiating all motor functions.
•  Broca's area: located on the left side of the frontal lobe, this processes language by controlling the mouth, lips, and larynx (together responsible for the production of speech).

The majority of the frontal lobe is dedicated to what are called associative areas —areas of the brain from which we receive our ability to think creatively, problem solve, make judgments and reflect upon events.

(Adapted from PMI Memoryzine, 2008)

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Temporal lobe—the lobe responsible for processing auditory information from the ears and relaying it to both the parietal and frontal lobes.  The temporal lobe gives us our musical abilities and houses some peripheral language and speech functions.

Also residing in the temporal lobes are the hippocampus, which guides short-term memory formation, as well as the retention of auditory and visual memories; and the amygdala, which communicates heavily with the hippocampus to initiate social behavior, primarily fear and anxiety responses, and manages sexual drives. It is believed that these two areas, combined with the temporal lobes’ other functions, come together to lend humans their sense of individual identity.

(Adapted from PMI Memoryzine, 2008)

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Parietal lobe—this lobe gives us our sense of touch, the ability to understand form through touch and our recognition of stimuli from our own body’s pain, temperature, pressure, etc. It also aids in some speech and visual functions.

(Adapted from PMI Memoryzine, 2008)

Back to Top

Occipital lobe—a lobe dedicated almost entirely to managing vision and its associated functions. It receives and processes all visual stimuli delivered by the optic nerves and via the thalamus, and relays the processed information back through the midbrain, inferior temporal lobe, association areas of the parietal lobe, and the frontal lobe. A lesion in the visual cortex can produce a wide range of symptoms, from not being able to see in your peripheral field of view, to complete blindness.

(Adapted from PMI Memoryzine, 2008)

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Memory

 

To fully understand K.C. and H.M. and their medical conditions, it is first important to have some background knowledge pertaining to memory and how it works.

 

What is Memory?

 

Memory is a function of the brain that allows people to store and retrieve information, personal experiences and procedures, such as skills or habits.  There are many different types of memory, as well as different methods for information storage and retrieval.

 

Types of Memory

 

Memory is split into two main categories; Explicit Memory and Implicit Memory.  Explicit Memory includes Semantic and Episodic Memory, while Implicit Memory includes Procedural Memory.

 

Explicit Memory	Also known as ‘Declarative Memory’; is memory for previous experiences and information that must be intentionally and consciously recalled.  Two types of explicit memory are Semantic Memory and Episodic Memory.
Semantic Memory	Memory for conceptual and factual knowledge that is not associated with a particular experience, such as word meanings or academic knowledge
Episodic Memory	Also known as ‘Autobiographical Memory’; is memory for events specific to an individual that uniquely define their life
Implicit Memory	Also known as 'Procedural Memory'; is memory that is not consciously or intentionally recalled, but is required to perform tasks
Procedural Memory	Memory allowing for learning of new skills and acquiring of habits

 

 

How Memories are Stored

 

Memory is generally split into three categories: Sensory Memory, Short Term or Working Memory and Long Term Memory.

 

Sensory memory acts to buffer stimuli received through the senses.  Each sensory channel has its own sensory memory; for visual stimuli—Iconic Memory, for sound stimuli—Echoic Memory, for touch stimuli—Haptic Memory (Harish, 2007).  Attention is required for sensory stimuli to be passed from sensory memory into short-term memory (Harish, 2007).

 

Short Term or Working Memory acts as a temporary storage space for incoming information.  Short Term Memory decays rapidly (within minutes) and has a limited capacity.  Studies have shown that Short Term memory is capable of retaining seven pieces of information, plus or minus two.  This is why chunking information can lead to a higher Working Memory retention rate (Harish, 2007).  Repeated exposure to a stimulus or the rehearsal of a piece of information in Short Term Memory is required to transfer it into Long Term Memory (Harish, 2007).  Interference—performing a task that prevents rehearsal of information retained in Short Term Memory—causes disturbances in Short Term Memory and the transfer of information from Short Term to Long Term Memory (Harish, 2007).

 

Long Term Memory is responsible for storage of information over a long period of time.  Some argue that information that has been successfully transferred from Short Term to Long Term Memory is permanently fixed in the brain.  Unlike Working Memory, there is little, if any, decay associated with Long Term Memory (Harish, 2007).  Forgetting may instead be connected to increasing difficulty in accessing certain memories.  Therefore forgotten information may simply be information that is unable to be retrieved (Harish, 2007).

 

Brain Areas Necessary for Memory Storage

 

First of all, the brain is divided into two hemispheres; the Left Hemisphere and the Right Hemisphere.  The two hemispheres are divided by the Longitudinal or Sagittal Fissure and are made up of four lobes, the Frontal Lobe, the Temporal Lobe, the Parietal Lobe and the Occipital Lobe.  Functionally, each lobe is remarkably distinct from the others (Martin, 2003).

 

To obtain a general idea of the location and function of certain brain structures associated with memory, click on either 'Ride Side View of the Brain', 'Dorsal (Top) View of Limbic System', or 'Sagittal Section Through the Brain'.  Or you may look at the following link for further interactive exploration of the brain and its various functions: http://www.bbc.co.uk/science/humanbody/body/interactives/organs/brainmap/index.shtml

K.C.—An Amazing Memory Impaired Individual

 

Have you ever wondered what life would be like if you couldn’t remember anything?  A complete lack of memory for recent, as well as past information and events is something that K.C. copes with on a daily basis. 

 

K.C. is a 57 year old Canadian suffering from both anterograde and retrograde amnesia.  Hence, as well as being unable to formulate new memories, he is unable to recall his past life events.  A motorcycle accident, at the age of 30, resulted in a head trauma that severely damaged the medial temporal lobes of K.C.’s brain and left him with no memory.

Due to his unique memory condition, K.C. has gained the interest of many researchers and scientists.  Case studies testing K.C.’s recall and learning abilities have greatly contributed to the science and understanding of memory, as well as aiding in establishing the function of certain brain structures.  A second individual who has had a large impact on neuropsycology and memory research is H.M. 

In 1927 a head injury, resulting from a bicycling accident, left H.M. with severe epilepsy.  To eliminate H.M.’s seizures, Dr. Scoville—a surgeon in Hartford—removed parts of H.M.’s medial temporal lobe on both sides of his brain.  Two-thirds of H.M.’s hippocampal region, as well as his amygdala were removed in the surgery.  Although the surgery was successful in curing his seizure problems, it also eliminated his ability to make and store new memories, rendering H.M. an anterograde amnesic. 

 

K.C.’s Family Portrait

 

(Rosenbaum et al., 2005)

K.C. is located at the far right of this photo