Higher Intellectual functions

HIGHER INTELLECTUAL FUNCTIONS

Higher intellectual functions are very essential to make up the human mind. These functions are also called higher brain functions or higher cortical functions. The extensive outer layer of gray matter in cerebral cortex is responsible for higher intellectual functions. Conditioned reflex forms the basis of all higher intellectual functions.

LEARNING

DEFINITION

Learning is defined as the process by which new information is acquired. It alters the behavior of a person

on the basis of past experience.

CLASSIFICATION OF LEARNING

Learning is classified into two types:

1. Non-associative learning

2. Associative learning.

1. Non-associative Learning

Non-associative learning involves response of a person to only one type of stimulus. It is based on two factors:

i. Habituation

ii. Sensitization.

i. Habituation

Habituation means getting used to something, to which a person is constantly exposed. When a person

is exposed to a stimulus repeatedly, he starts ignoring the stimulus slowly. During first experience, the event (stimulus) is novel and evokes a response. However, it evokes less response when it is repeated. Finally, the person is habituated to the event (stimulus) and ignores it.

ii. Sensitization

Sensitization is a process by which the body is made to become more sensitive to a stimulus. It is called

amplification of response. When a stimulus is applied repeatedly, habituation occurs. But, if the same

stimulus is combined with another type of stimulus, which may be pleasant or unpleasant, the person

becomes more sensitive to original stimulus. For example, a woman is sensitized to crying sound

of her baby. She gets habituated to different sounds around her and sleep is not disturbed by these sounds. However, she suddenly wakes up when her baby cries because of sensitization to crying sound of the baby. Thus, sensitization increases the response to an innocuous stimulus when that stimulus is applied after another type of stimulus.

2. Associative Learning

Associative learning is a complex process. It involves learning about relations between two or more stimuli at a time.

MEMORY

DEFINITION

Memory is defined as the ability to recall past experience or information. It is also defined as retention of learned materials. There are various degrees of memory. Some memories remain only for few seconds, while others last for hours, days, months or even years together.

ANATOMICAL BASIS OF MEMORY

Anatomical basis of memory is the synapse in brain. Synapse for memory coding is slightly different from

other synapses. Two separate presynaptic terminals are present here. One of the terminals is primary presynaptic terminal, which ends on postsynaptic neuron as in conventional synapse. This terminal is called sensory terminal, because sensations are transmitted to the postsynaptic neuron through this terminal. Other presynaptic terminal ends on the sensory terminal itself. This terminal is called facilitator terminal. When, sensory terminal is stimulated alone without facilitator terminal, the firing from sensory terminal leads to habituation, i.e. the firing decreases slowly. On the other hand, if both the terminals are stimulated, facilitation occurs and the signals remain strong for long period, i.e. for few months to few years.

PHYSIOLOGICAL BASIS OF MEMORY

Memory is stored in brain by the alteration of synaptic transmission between the neurons involved in memory. Storage of memory may be facilitated or habituated depending upon many factors, such as neurotransmitter, synaptic transmission, functional status of brain, etc.

Facilitation

Facilitation is the process by which memory storage is enhanced. It involves increase in synaptic transmission and increased postsynaptic activity. Often, facilitation is referred as positive memory.

The process involved in facilitation of memory is called memory sensitization.

Habituation

Habituation is the process by which memory storage is attenuated (attenuation = decrease in strength, effect or value). It involves reduction in synaptic transmission and slow stoppage of postsynaptic activity. Sometimes, habituation is referred as negative memory.

Basis for Short-term Memory

Basic mechanism of memory is the development of new neuronal circuits by the formation of new synapses and facilitation of synaptic transmission. Number of presynaptic terminals and size of the terminals are also increased. This forms the basis of short-term memory.

Basis for Long-term Memory

When neuronal circuit is reinforced by constant activity, memory is consolidated and encoded into different areas of the brain. This encoding makes memory a permanent or a long-term memory.

Sites of Encoding

Hippocampus and Papez circuit (closed circuit between hippocampus, thalamus, hypothalamus and

corpus striatum) are the main sites of memory encoding. Frontal and parietal areas are also

involved in memory storage.

Experimental Studies of Memory – Aplysia

Most of the experimental studies of memory and learning are based on the research carried out in the sea

hare (sea snail) called Aplysia. This animal is useful in brain research because it has a simple uncomplicated nervous system that can be easily approached in living animal with simple dissection. Another advantage of this snail is that the individual nerve cells are large and

brightly colored. Nobel laureate, Eric Kandel was the pioneer to use Aplysia for the studies of memory and learning.

CHEMICAL OR MOLECULAR BASIS OF MEMORY

Memory Engram

Molecular basis of memory can be explained by memory engram. Memory engram is a process by which

memory is facilitated and stored in the brain by means of structural and biochemical changes. Often, it is also called memory trace.

Molecular Basis of Facilitation

In this process, the neurotransmitter serotonin plays major role. Calcium ions increase the release of

serotonin, which facilitates the synaptic transmission to a great extent, leading to memory storage.

Molecular Basis of Habituation

Habituation is due to passive closure of calcium channels of terminal membrane. Hence, the release of

transmitter decreases, resulting in decrease in number of action potential in the postsynaptic neuron. So, the signals become weak and weakening of signals leads to habituation.

 

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