Higher Intellectual Functions

HIGHER INTELLECTUAL FUNCTIONS LEARNING DEFINITION Learning is defined as the ability to alter behavior on the basis of past experience. Memory is the ability to recall the past experience. i. Habituation Habituation means getting used to. When a person is exposed to a stimulus repeatedly, the person starts ignoring the stimulus slowly. During the first experience, the event (stimulus) is novel and evokes a response.

TYPES OF LEARNING

Learning is of two types namely: 1. Non-associative learning 2. Associative learning.

1. Non-Associative Learning This involves response of a person to only one type of stimulus. It depends upon two factors namely: i. ii.

Habituation Sensitization.

i. Habituation Habituation means getting used to. When a person is exposed to a stimulus repeatedly, the person starts ignoring the stimulus slowly. During the 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 When a stimulus is applied repeatedly, there is habituation. But if the same stimulus is combined with another type of stimulus, which may be pleasant or unpleasant, the person becomes more sensitive to the original stimulus. This is called the sensitization. For example, a lady gets habituated to different sounds around her and sleeps. But, she promptly wakes up when her baby cries. 2. Associative Learning This is a complex process. And, it involves learning about relations between two or more stimuli at a time. The classic example of associative learning is the conditioned reflex, which is described later in this chapter.

MEMORY

DEFINITION Memory is defined as the ability to recall the past experience. There are various degrees of memory. Some memories remain only for few seconds, while others last for hours. days, months or years together. TYPES OF MEMORY Memory can be classified into different types namely: 1. Sensory memory

2. Primary memory 3. Secondary memory. 1. Sensory memory This is the ability to retain sensory signals in the sensory areas of brain. The sensory signals are retained only for a short period after the actual sensory experience i.e. few hundred milliseconds. But, the signals can be replaced by new sensory signals in less than one second. This is the initial stage of memory. 2. Primary memory It is the memory of facts, words, numbers, letters or other information received for a few seconds to few minutes at a time. For example, after searching for a telephonenumber in the directory, we remember the number for a short while. After appreciating a beautiful scenery, the details could be recalled for sometime or days. Afterwards it disappears from the memory. The characteristic feature of this type of memory is that the information is available for recall easily from memory store itself. One need not search or squeeze through the mind and, this memory can be easily replaced by new bits of memory i.e.. by looking into another telephone number, the first one might disappear. 3. Secondary Memory This is the storage of information in the brain for a longer period. The information could be recalled after hours, days, months or years. This is also called fixed memory or permanent memory. Short Term and Long Term Memories • Memory is also classified into short term memory and long term memory. • Short term memory is applicable to the recalling of events of hours or days. • Long term memory is the recalling of the events of weeks, months or years.

I PHYSIOLOGICAL BASIS OF MEMORY Basis for Short Term Memory • Basic mechanism of memory is the development of new neuronal circuits by the formation of new synapses. • The number of presynaptic terminals and the size of the terminals may also be increased. This is the basis of short term memory. Basis for Long Term Memory • When the neuronal circuit is reinforced by using it often, the memory gets consolidated and becomes permanent or long term memory, and this gets encoded into different areas of the brain. Sites of Encoding • Hippocampus and the Papez circuit (the closed circuit among hippocampus, thalamus, hypothalamus and corpus striatum) are the main sites for memory encoding. • Frontal and parietal areas are also important areas for memory. II ANATOMICAL BASIS OF MEMORY • Synaptic terminal for memory coding is slightly different from other synapses. • Two separate presynaptic terminals are involved. • One of the terminals is the primary presynaptic terminal. This ends on postsynaptic neuron. • This terminal is called sensory terminal, as the sensations are transmitted to postsynaptic neuron through this terminal. • The other presynaptic terminal ends on the sensory terminal itself. • This second terminal is called facilitator terminal. • If sensory terminal alone is stimulated without facilitator terminal, the firing from sensory terminal leads to habituation. • On the other hand, if both the terminals are stimulated, the signals remain strong for long duration i.e., for few months to few years. This is called facilitation.

III CHEMICAL OR MOLECULAR BASIS OF MEMORY Habituation: • Habituation is due to passive closure of calcium channels of terminal membrane. • Hence, the release of transmitter is less and action potential is in less number. • So, the signals become weak. The weakening of the signals is called habituation. Facilitation: This occurs in the following manner: 1. Stimulation of facilitator neuron along with sensory neuron causes release of serotonin from facilitator terminal on sensory terminal. 2. Serotonin binds with serotonin receptor. 3. Now, the serotonin receptor complex activates the enzyme adenyl cyclase in the terminal membrane. 4. This causes formation of cyclic AMP in sensory terminal. 5. Cyclic AMP activates the protein kinase. 6. The protein kinase causes phosphorylation of potassium channels in the terminal membrane. 7. This blocks the exit of potassium ions. 8. So, the action potential continues for days or weeks or still longer. 9. Prolonged action potential causes prolonged activation of calcium pores thereby allowing large amount of calcium to enter sensory terminal. 10. The calcium ions further enhance the release of transmitter Le. serotonin thus facilitating synaptic transmission to a great extent leading to memory. The overall facilitated circuit is called memory engram or a memory trace.

IV CONSOLIDATION OF MEMORY • The primary memory becomes secondary memory by consolidation i.e., the permanent facilitation of synapses. • This is possible by rehearsal mechanism i.e.rehearsal of same information again and again accelerates and potentiates the degree of transfer of primary memory into secondary memory.

APPLIED PHYSIOLOGY - ABNORMALITIES OF MEMORY 1. Amnesia Loss of memory is known as amnesia. There are two types of amnesia viz: i. ii.

Anterograde amnesia Retrograde amnesia.

i.

Anterograde amnesia: • It is the failure to establish new long term memories. • This usually occurs due to lesion in hippocampus. Retrograde amnesia: • Failure to recall past remote long term memory is called retrograde amnesia. • It occurs in temporal lobe syndrome.

ii.

2. Dementia

Definition • Progressive deterioration of intellect, behaviour and personality as a consequence of diffuse disease of the cerebral hemispheres, maximally affecting the cerebral cortex and hippocampus. • Distinguish from delirium which is an acute disturbance of cerebral function with impaired conscious level, hallucinations and autonomic

over activity as a consequence of toxic, metabolic or infective conditions. • Dementia may occur at any age but is more common in the elderly, accounting for 40% of long-term psychiatric in-patients over the age of 65 years. • A recent study shows an annual incidence rate of 187/100 000 persons. Dementia is a symptom of disease rather than a single disease entity. • When occurring under the age of 65 years it is labeled 'presenile' dementia. This term is artificial and does not suggest a specific aetiology. Clinical course: The rate of progression depends upon the underlying cause. The duration of history helps establish the cause of dementia; Alzheimer's disease is slowly progressive over years, whereas encephalitis may be rapid over weeks. Dementia due to cerebrovascular disease appears to occur 'stroke by stroke'. All dementias show a tendency to be accelerated by change of environment, intercurrent infection or surgical procedures.

CONDITIONED REFLEXES DEFINITION • Conditioned reflex is a reflex response acquired or learnt by experience. Conditioned reflex is the basis of learning. • The unconditioned reflex is the inborn reflex. • There is no need of previous experience for this reflex. • The example is the salivary secretion by placing the food in the mouth. But, the conditioned reflex is acquired after birth and requires previous experience. TYPES OF CONDITIONED REFLEXES The conditioned reflexes are of two types namely:

I. Classical conditioned reflexes. II. Instrumental conditioned reflexes. Classical Conditioned Reflexes Classical conditioned reflexes are those reflexes, which can be established by a conditioned stimulus followed by an unconditioned stimulus.

Types and Properties of Classical Conditioned Reflexes Classical conditioned reflexes are divided into 2 groups namely: A. Positive or excitatory conditioned reflexes. B. Negative conditioned reflexes. This ciassification is according to the properties of the reflexes namely, the excitation or inhibition. POSITIVE CONDITIONED REFLEXES (EXCITATION OF CONDITIONED REFLEXES) There are three types of positive conditioned reflexes viz: 1. Primary conditioned reflex 2. Secondary conditioned reflex 3. Tertiary conditioned reflex Primary conditioned reflex – This reflex is established in the following way. • The animal is fed with food (Unconditioned stimulus). Simultaneously a flash of light (conditioned stimulus) is also shown. Both the stimuli are repeated for some days. • When the reflex is developed the flash of light (conditioned stimulus) alone causes salivary secretion without food (unconditioned stimulus). • Thus, the development of a conditioned reflex with one unconditioned stimulus and one conditioned stimulus is called primary conditioned reflex.

Secondary conditioned reflex• After establishment of a conditioned reflex with one conditioned stimulus, another conditioned stimulus is applied. • For example, a flash of light (first conditioned stimulus), a bell sound (second conditioned stimulus) and the food (unconditioned stimulus) are given. • After the development of the reflex, the second conditioned stimulusthe bell sound alone can cause salivary section. • The development of a conditioned reflex with one unconditioned stimulus and two conditioned stimuli is called secondary conditioned reflex. Tertiary conditioned reflexIn this, a third conditioned stimulus is added and, the reflex is established. But, the reflex with more than three conditioned stimuli is not possible. NEGATIVE CONDITIONED REFLEXES (INHIBITION OF CONDITIONED REFLEXS) The established conditioned reflexes can be inhibited by some factors. The inhibition is of two types namely: a. External or indirect inhibition. b. Internal or direct inhibition. External or indirect inhibition • The established conditioned reflex is inhibited by some form of stimulus, which is quite different from the conditioned stimulus. • It is not related to conditioned stimulus. For example, some disturbing factors like sudden entrance of a stranger, sudden noise, or a strong smell can abolish the conditioned reflex and inhibit salivary secretion. • The extra stimulus evokes the animal's curiosity and distracts the attention. Internal or direct inhibition: There are four ways in which, the established conditioned reflex is abolished by direct or internal factors, which are related to the conditioned stimulus.

1. 2. 3. 4.

Extinction of conditioned reflex Conditioned inhibition Delayed conditioned reflex or inhibition by delay Differential inhibition.

1. Extinction of conditioned reflex: • After establishing a conditioned reflex, the conditioned stimulus must be coupled with unconditioned stimulus now and then i.e., the conditioned stimulus must be reinforced by unconditioned stimulus. • If a conditioned stimulus is given repeatedly several times without reinforcing it by unconditioned stimulus, there is failure of conditioned reflex. • This is called the extinction of conditioned reflex. However, the reflex will not be abolished if the unconditioned reflex is also used in between. 2. Conditioned inhibition: • When a conditioned stimulus is effective e.g. the flash of light, along with this, if another conditioned stimulus i.e. a bell sound is applied suddenly, the response does not occur. • This is called conditioned inhibition. Of course, if both conditioned stimuli were given with unconditioned stimulus (food) repeatedly, the secondary conditioned reflex is developed. 3. Delayed conditioned reflex or inhibition by delay: • While establishing a conditioned reflex, after applying a conditioned stimulus (light or sound) the unconditioned stimulus (food) must follow immediately. • After applying the conditioned stimulus, if the unconditioned stimulus is applied after a long time, there will not be a response or the response will be delayed. • This is called delayed conditioned reflex and this property is called the inhibition by delay.

4. Differential inhibition: • When an animal is trained or conditioned for a particular type of stimulus, and if the stimulus is altered slightly, the response does not occur. • The animal is able to discriminate the difference. For example, the alteration in frequency of sound or intensity of light abolishes the conditioned reflex. • This is called differential inhibition.

Learning and memory form the physiological basis of the conditioned reflexes. SPEECH DEFINITION • Speech is an expression of thoughts by production of articulate sound, bearing a definite meaning. • It is one of the highest functions of brain. It is brought about by coordinated activity of different parts of brain, particularly the motor, sensory and psychic areas. • When a sound is produced verbally, it is called the speech. • If it is expressed by visual symbols, it is known as writing. • If visual symbols or written words are expressed verbally, that becomes reading. MECHANISM OF SPEECH • Speech depends upon the coordinated activities of central speech apparatus and peripheral speech apparatus. • The central speech apparatus consists of higher centers i.e., the cortical and subcortical centers. • The peripheral speech apparatus includes larynx or sound box, pharynx, mouth, nasal cavities, tongue and lips. • All the structures of the peripheral speech apparatus work in coordination with respiratory system, under the influences of the motor impulses from the respective motor areas of the cerebral cortex.

DEVELOPMENT OF SPEECH First Stage The first stage in the development of speech is the association of certain words with visual, tactile, auditory and other sensations, aroused by objects in the external world. The association of words with other sensations is stored as memory. Second Stage • New neuronal circuits are established during the development of speech. • When a definite meaning has been attached to certain words, pathway between the auditory area (Heschl area-41) and motor area for the muscles of articulation which helps in speech (Broca's area 44) is established. • The development of speech involves integration of three important areas of cerebral cortex namely, Wernicke's area, Broca's area and motor area of the dominant hemisphere. Role of Wernicke's area: • The understanding of speech begins in Wernicke's area that is situated in upper part of temporal lobe. • It sends fibers to Broca's area through a tract called arcuate fasciculus. Wernicke's area is responsible for understanding the visual and auditory information required for production of words. • After understanding the words it sends the information to Broca's area. Role of Broca's area: • Speech is synthesized in the Broca's area. • It is situated adjacent to the motor area responsible for the movements of tongue, lips and larynx necessary for speech. • By receiving information required for production of words from Wernicke's area, the Broca's area develops the pattern of motor activities required to verbalize the words.

• The pattern of motor activities is sent to the motor area. Role of motor area: • By receiving the pattern of activities from Broca's area, the motor area initiates the movements of tongue, lips and larynx required for speech. • Later, when the child is taught to read, auditory speech is associated with visual symbols (Area 18). • Then, there is association of the auditory and visual areas with the motor area for muscles of hand. • Now, the child is able to express the auditory and visual impressions in the form of written words. NERVOUS CONTROL OF SPEECH • Speech is an integrated and well-coordinated motor phenomenon, involves cortical and subcortical areas. • The subcortical areas concerned with speech are controlled by cortical areas of dominant hemisphere. • In about 95% of human beings the left cerebral hemisphere is functionally dominant and those persons are right handed. • Speech and handedness are always interrelated. Following are the motor and sensory cortical areas concerned with speech. A. Motor Areas 1. Broca's Area • This is the area 44. It is also called speech center, motor speech area or lower frontal area. It is situated in lower part of lateral surface of prefrontal cortex. • This area controls the movements of vocalization. So, this area is known as speech center. 2. Upper Frontal Motor Area • It is situated in the paracentral gyrus over the medial surface of the cerebral hemisphere. • This controls the coordinated movements concerned with writing.

B. Sensory Areas 1. Auditopsychic Area This area is situated in the superior temporal gyrus. It is concerned with storage of memories of spoken words. 2. Visuopsychic Area It is present in angular gyrus of the parietal cortex. It is concerned with storage of memories of the visual symbols. C. Wernicke's Area • This area is situated in the upper part of temporal lobe. • It also plays an important role in speech. • It is responsible for understanding the auditory and visual information about any word and sending the information to Broca's area. APPLIED PHYSIOLOGY: DISORDERS OF SPEECH Following are the disorders of speech: A. Aphasia B. Anarthria or Dysarthria C. Agnosia. A. Aphasia Aphasia means loss of speech. It may involve the expression of spoken word or written word or both. Aphasia is not due to paralysis of muscles of articulation. It occurs mostly due to the defect in the higher cortical areas. Types of Aphasia 1. Sensory aphasia: • It is the inability to understand words or symbols. It may be auditory aphasia or visual aphasia.

• Auditory aphasia is the inability to understand the spoken words. This is also called word deafness. • This is due to the lesion in auditopsychic area. • Visual aphasia is the difficulty in understanding the written symbols. • It is also called word blindness and occurs due to the lesion in visual psychic area. 2. Motor aphasia or verbal aphasia: This is the inability to use the words for expression of thought. There is defect in the utterance of individual words. It is due to the defect in pathways between speech center and excitomotor cortex. 3. Auditory aphasia or Syntactical aphasia or Word deafness: This is the inability to understand the spoken words. This occurs due to the lesion in auditory areas (41, 42). The subject is able to read or write with difficulty but, he cannot speak sensibly. He utters words in short phrases. The sentences are broken and meaningless. This type of speech is known as jargon speech. 4. Semantic aphasia: It is characterized by more difficulty in uttering the words. The sentences become short and jerky and the subject fails to follow the facts while talking. At the same time, the subject is unable to understand the general meaning of what is talked to him. Sometimes, the subjects fail to understand their own utterances. 5. Agraphia: Agraphia means the inability to write, though there is no defect in the muscles of the hand concerned with writing. The subject can read and speak. Agraphia is due to the defect in the connection between the writing center and excitomotor center.

6. Word blindness: In this, the subject is unable to read the written or the printed words. However, the person is able to speak and write. This is due to the defect in visual cortex. 7. Cortical aphasia: It is the defect in speech function, on the whole. It is associated with intellectual defects. This is due to the lesion of association fibers at subcorticallevel, concerned with audition, vision, somatic activities etc. 8. Nominal aphasia: This is the inability in naming the objects. This is due to defect in visual cortex. B. Anarthria or Dysarthria This is the inability or difficulty to speak. This is due to the paralysis or ataxia of muscles involved in articulation. The psychic aspect of speech is not affected. The spoken and written words are understood. C. Agnosia The inability to understand the words or the inability to recognize a known object is called agnosia.