Higher Order Brain Functions:Principle of Mass Action, Long-term memory

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Neurological Basis of Behavior (PSY - 610)

Lesson44

Higher Order Brain Functions

Objectives:

The students would be familiarized with the role of higher order brain functioning in learning, memory

and amnesias.

Brain correlates:

· Brain correlates of Learning and Memory, Amnesia, Verbal, Non verbal memory,

· Famous case of Amnesia, H.M.

Memory is one of the puzzles where biologist, physiologists, neurologists started working early on

Krech (1973) spent a lifetime investigating memory believes that memory is one of the most intriguing

phenomenon. There are many hypotheses and there are many frustrations for those working in this field.

Lashley was pioneer in the area of locating engrams- basically he was a zoologist trying to locate where

memories are " I sometimes feel, in reviewing the evidence on the localization of the memory trace, that

the necessary conclusion is that learning is just not possible. (Lashley 1950)

Memory is defined as information stored in the brain because of sensory and other experience

(Bridgeman 1992, p324) and learning is the acquisition of new memories. However, where exactly is

happening and how? Is there a specific location or diffuse connection and locations?

Lashley formulated two principles: the Principle of Equipotentiality and Principle of Mass Action

Principle of Equipotentiality:

Lashley trained rats to run the maze. The animals learned to discriminate between the light and dark

alleys. They were rewarded for light alleys and punished forgoing into the dark alleys. Lesioning

various parts of the brain, he found that disruption of learning took place after lesions of the visual

cortex. He reported that for retention of visual tasks Visual cortex important. Various parts of cortex

contribute to memory at least for complex behaviors. No one part is more or less specialized than other"

Neurons within a given sensory area is capable of participating in memory formation- all are

equipotential in contributing to the retention of a task. Memories are also discretely located within each

sensory cortex (though diffusely spread in that area) There are also memories for the specialized sensory

function.

Principle of Mass Action:

Lashley's rats were trained on complex tasks utilizing information from various sensory modalities,

requiring visual cues, somato-sensory cues, kinesthetic and even auditory cues. This involves mass

action. Thus, information from all cortical areas is integrated to form complete memories. After the

learning had taken place Lashley lesioned parts of the cortex and found that the greater the extent of the

lesion, the greater the deficits in memory. Retention is related to the size of the cortical areas removed.

Thus, it appeared that cortical area is not important only the extent of damage. Therefore, cortex works

as a whole, the more cortex involved in learning the better it is. The same principle holds for man and

for rats. As an example, soldiers with head bullet wounds exhibited lower IQ on tests performance, and

the lowering of I.Q depended upon the overall amount of brain damage. The amount of remaining

cortex is more important than the region states Grafman and his colleagues 1986)

There are many more questions to memory. It is intriguing to how we learn, forget, how we remember

friends, their faces, spellings of names or generally, telephone numbers etc. The question is also why

older people remember events long past better than immediate past, where are our memories located?

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There are many such questions.

Why do different areas store different part of the memory picture, how does it get integrated. One

piece missing how the defect is covered, or compensated.

In the 1950's two different memory storage systems, the Short Term Memory (STM) and the Long

Term Memory (LTM) were hypothesized. Memories are retained in the STM(stored temporarily) when

the physiological changes to store in the long term memory are taking place, the STM memories are

transferred to LTM.

Short-term memory

repeated thinking and reviewing

Long-term memory

Hebb one of the pioneers of neurosciences and of memory research stated that memories remain in STM

temporarily. The reverberating neural activity (neural activity, which goes, round and produces

structural changes in synapses) leads to LTM storage. Thus, the changes in neuronal biochemical

structure are the basis of LTM storage. He proposed a Two-stage memory theory is supported by

everyday evidence that unless you keep repeating telephone number it becomes difficult to recall it!

Cross modal transfer:

It is possible to learn with one sensory mode and use what is learnt and retained, in another mode. For

example, the visual scanning of mazes takes place, then one can go through it using the kinesthetic

mode. Humans and higher primates can do that easily but lower animals cannot transfer information

from one modality to another. If memories were diffusely stored then lower animals should also be able

to do the same

Problems and Issues in testing memories:

a) There is no adequate method to identify where memories are stored, where memories stored not

known effectively even after so many years of research,

b) Performance not memory may be affected (if you remember there was a famous joke that if you cut

frog legs the frogs forget to hop across lines--- performance not memory was affected by cutting the

legs)

c) How do we know that connections of other areas are not damaged by lesions to one area? Lesion in

one area may alter connection in other,

d) Lastly, is what we assess if the loss of memory or the loss of retrieval of memory?

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Biological Systems and Memory:

Researches using single cell recordings have shown that learning changes single cells. There are

measured increases in calcium in neurons, decreases in potassium flow, increases in number of certain

synaptic receptors, changes in RNA and proteins. Impaired learning may be due to the deficits in

biochemistry.

RNA:

These are the memory code molecules. There are qualitative and quantitative changes in measures of

RNA and protein synthesis in animals, which have learnt a task. Heredity is memory passed on from

one to another generation. The DNA is the template for RNA-, which determine the structure of

proteins. Hyden and Colleagues (1962) trained rats to walk on a tight rope as compared to normals.

There was increase in increase in RNA in brain cell nuclei. Glassman and colleagues (1974) showed

that changes in RNA and proteins were found after learning a shock avoidance task. Shock avoidance

where the rats had to jump onto a platform at the sound of a buzzer, whereas the controls had a buzzer

but no shock/ and or no platform to jump. These rats were injected with labeled Uri dine (precursor for

RNA), or labeled lysine (precursor for protein), 30 minutes before the experiment. The amount of Uri

dines incorporation decreased with time i.e. RNA synthesis decreased after training and lysine increased

after training. RNA coding for new protein. Labeled Lysine injected carried into cortex and

hippocampus with acquisition. Interesting experiments have also been carried out where rats, chicks and

other species were trained and learnt a task, these animals were decapitated and their brains

homogenized and injected into the normal rats. It was found that the injected animals learnt faster than

untrained or un-injected rats.

Protein synthesis:

Researches on single cell basis of learning have indicated evidence that Proteins synthesis is a necessary

step in long-term memory. Proteins synthesis modifies characteristics and properties of neurons. Drugs

that inhibit protein synthesis impair LTM storage but not STM. The increased inhibition leads to

increased deficits in learning (Bennet et al, 1977). Anisomycin blocks protein synthesis blocked rats

memory of location of the shock but not the memory of location of food!

Other important bio-chemicals are Cyclic Amp, ACTH, Vasopressin, Acetylcholine and NE

Other Influences on Learning and memory:

Stress interferes with learning and retrieval of information. We all are familiar with Blockade before

important paper! Electroconvulsive therapy blocks protein synthesis

Hebb's consolidation theory time required for STM to LTM any interference with consolidation would

result in disruption of long-term recall. If there is a head injury then memory of events prior to injury

lost (retrograde amnesia), destroyed as evidence indicates that a small reminder brings back memories

.In head trauma memory returns after delay or under tranquilizers.

ECT affects both long term and short-term memories: Kalat (1980) "ECT interferes with memories that

are active at the time of ECS regardless of the fact whether formed recently or long ago"

Plasticity and the nervous system

Experiments by Hubel and weasel have shown that anatomical changes take place in the visual cortex

with experiences. Horizontal goggles worn by kittens during early period of development lead to firing

of neurons when horizontal stripes are seen as adults.

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Similarly, if one eye receives more stimulation, the brain area for that eye is enlarged (more neurons

respond)

Shock to the foreleg of young kittens led to a greatly enlarged somato-sensory cortical area (Increased

stimulation led to increased areas for responding).

Merzenich carried out an experiment where he joined the third and index finger by sewing them

together, the area for this "one" finger becomes large. If the thumb is removed the areas for thumb in the

cortex becomes smaller. MRI's studies of violinist's brains showed that their cortical auditory areas

were enlarged as compared to normals.

Super Plasticity in growing Brain?

There have been studies which have shown that an early start e.g. for musicians, for language

proficiency, for players, for gymnasts, there is need to start early. As the information, being sent to the

sensory cortices when learning is taking place. In language learning, the left hemisphere growth spurt is

recorded on EEG between 2-4 years of age, and another 12-15 years again only in the left hemisphere.

There is increasing research in the early development and the neuronal stimulation, nerve growth factor,

and stem cell research.

Brain correlates of Learning and Memory, Amnesia, Verbal, Non-verbal memory, tests

Amnesia is a memory disorder, and patients suffering from Amnesia have been studied to find out more

about how memory works. One of the most famous cases of amnesia is

H.M: pure amnesic: H.M. had severe epileptic seizures and for treatment of epilepsy, surgery was

carried out when he was 27 years old. In addition, after the surgery he has been in the time freeze of

being stuck at 27 (even 40 years later) HM has amnesia for events prior to surgery, and has no LTM. He

actually lives in the present, in STM. He ahs no IQ loss as assessed by IQ tests. He has been tested for

memory using the mirror drawing task, the digit span test, Block tapping memory span test, Incomplete

pictures test, and even eye blink Pavlovian type conditioning response. He has damage in the temporal

region and this has provided evidence of the importance of temporal lobe (and hippocampus) in

memory.

AMNESIA

Anterograde:loss of ability to learn new information. The amnesic can remember events before

surgery or injury. The complex perceptual motor learning abilities however are intact in these

patients. Karsakoff's syndrome is the severest form of Anterograde Amnesia, where damage is

to the mammilliary bodies and temporal lobe

Retrograde. This form of amnesia is inability to remember event, which had occurred before

brain damage. Confabulation is creation of pseudo memories to fill gaps.

Alzheimer's disease is one of the major diseases, which leads to severe memory loss. This is the

most common cause of dementia ( memory and intellectual impairment) research has provided

evidence of Neurofibrils, amygdloid plaques, neural degeneration, also reduction in ACH as the

underlying pathology in Alzheimer's Studies on amnesiacs have shown:

1. Hippocampus is not the location of Long term memory nor is it important for retrieval of long

term memories

2. It is also not the location for immediate memories

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3. Hippocampus is involved in transforming STM to LTM

Studies have also shown the importance of mammilliary bodies, and the Dorsomedial Thalamus in

memory.

References:

1. Carlson N.R. (2005) Foundations of Physiological Psychology Allyn and Bacon, Boston

2. Pinel, John P.J. (2003) Biopsychology (5th edition) Allyn and Bacon Singapore

3. Bloom F, Nelson and Lazerson (2001), Behavioral Neuroscience: Brain, Mind and Behaviors (3rd

edition) Worth Publishers New York

4. Bridgeman, B (1988) The Biology of Behaviour and Mind. John Wiley and Sons New York

5. Brown,T.S. and Wallace.(1980) P.M Physiological Psychology. Academic Press New York.

6. Bradshaw J.L. and Mattingley, J.B. (1995) Clinical Neuropsychology: Behavioral and Brain

Sciences. ACADEMIC PRESS

7. Bridgeman, (1992) p324, graham 354, Carlson, Brown and Wallace 474, Pinel 268

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