Cerebral Cortex Prof K Sivapalan Lobes of Cerebrum

Cerebral Cortex Prof. K. Sivapalan

Lobes of Cerebrum • Frontal lobe: anterior to central sulcus and above the lateral sulcus. • Parietal lobe: behind central sulcus above the level of the lateral sulcus upto parieto-occipital sulcus • Temporal lobe: below the lateral sulcus up to preoccipital notch • Occipital lobe: behind the line connecting the parieto-occipital sulcus and preoccipital notch • Insula: under parietal and temporal opercula. 2/26/2021 Cerebral Cortex 2

Higher Functions • Higher functions are learning, memory, judgment, language, and other functions of mind. • Important characteristic of animals is to alter behavior on the basis of experience- learning. • Learning is acquisition of information, skills and attitude. • Memory is the retention and storage of that are learnt. 2/26/2021 Cerebral Cortex 3

Location of Primary Functional and Association Areas. 2/26/2021 Cerebral Cortex 4

Functional Areas of the Cortex. 2/26/2021 Cerebral Cortex 5

Parieto-occipito-temporal Association Area. • THIS INCLUDES AREAS FOR: • Analysis of the spatial coordinates of the body. • Area of language comprehension- Wernike’s area. • Area for initial processing of visual language [reading]. • Area for naming objects. • Area for processing auditory language. 2/26/2021 Cerebral Cortex 6

Prefrontal Association Areas. • Plans complex patterns and sequence of movements. • Carries out the thought process of the mind. Judgment, morality, prediction of future etc. • Stores working memory. 2/26/2021 Cerebral Cortex 7

Limbic Association Area • Concerned with emotions, behavior and motivation. • Anterior pole of the temporal lobe, ventral portion of the frontal lobe, and the cingulate gyrus. 2/26/2021 Cerebral Cortex 8

Area for Recognition of Faces. • Medial under side of both occipital lobes and medioventral surface of the temporal lobes. • Area allocated indicates the significance of associations with other people. 2/26/2021 Cerebral Cortex 9

Attention of the Body. • Lesions of posterior part of inferior temporal lobe results in unilateral inattention and neglect. • No visual, auditory or somasthetic defects. • Stimuli from opposite side of the body and the space around these parts are ignored. • Shave, dress wash only half of their bodies. The other side does not come into attention. 2/26/2021 Cerebral Cortex 10

Comprehensive Interpretive Function. • All sensory inputs are processed and sent to Wernike’s area. • It is situated at the posterior part of superior gyrus of the temporal lobe. • When there is lesion of this area, vision, hearing and other sensations are normal • But cannot recognize thought conveyed by them. 2/26/2021 Cerebral Cortex 11

Specialization of Left Cerebral Hemisphere • Usually the left hemisphere is specialized in language. • That is understanding spoken or written words and expressing by speech or writing. • These processes are known as categorization and symbolization. • Therefore it is called Categorical hemisphere. • Lesions in this hemisphere causes language disorders. • Patients are disturbed about the disability and depressed. 2/26/2021 Cerebral Cortex 12

Language Disorders • Aphasia- abnormalities not caused by defects of vision or hearing or to motor paralysis. • Fluent aphasia- lesion in Wernike’s area- excessive talk with jargons and neologisms but no sense. Patient also fails to make sense of spoken or written words. • Nonfluent aphasia- lesion in Borca’s area- no or few words produced. • Anomic aphasia- lesion in angular gyrus – no defect in speech or understanding spoken massage but written and pictural massages cannot processed and transmitted. 2/26/2021 Cerebral Cortex 13

Specialization of Right Cerebral Hemisphere. It is specialized in spatiotemporal relations. Identification of objects, faces and musical themes. This is representation. Therefore it is called the representational hemisphere. • Lesions cause agnosia – one example is astereognosis. • Patients are unconcerned about the inability and sometimes euphoric. They are unable to recognize emotions of others. • • 2/26/2021 Cerebral Cortex 14

Specialization of Cortices. • 91 % of the people are right handed. • Of these 96 % have the left as categorical hemisphere [? dominant]. • Of the left-handers, 70 % have left hemisphere as categorical, 15 % the right and the other 15 % show no clear lateralization. • Inability to learn to read is very common among lefthanders. • Some unusual feature in left hemispheres may have switched over the development of right hemisphere. • But the spatial talents may be well above the normal in left-handers- musicians, artists and mathematicians. 2/26/2021 Cerebral Cortex 15

Habituation and Sensitization • Habituation • Simple form of learning by repeating a neural stimulus many times. • The first stimulus evokes “what is it” response. • The response reduces with repeated stimuli and finally it is completely ignored. • Sensitization • Repeated stimuli produce greater response- if coupled with pleasant or unpleasant stimulus once or more times. • Arousal value- mother sleeps through many noises but aroused by slight cry of her baby. 2/26/2021 Cerebral Cortex 16

Conditioned Reflexes. • Salivation on placement of food is a normal reflex. [meat is unconditioned stimulus- US] • In Pavlov’s experiment, bell is conditioned stimulus [CS]. • Several stimuli can be conditioned. • If CS is repeated without US, extinction or internal inhibition occurs. • If it is disturbed by external stimuli, external inhibition occurs. • Reinforcing the CS from time to time can keep the reflex indefinitely. 2/26/2021 Cerebral Cortex 17

Operant Conditioning. • Animal is trained to “operate” in order to obtain reward or avoid punishment. • US is reward or punishment. • CS is the stimulus that signals and alerts the animal to perform the task. • If eating is coupled with unpleasant feeling by injection or electrical stimulus, food aversion conditioning occurs which can be very strong. • Survival value of this is avoidance of poisoning. 2/26/2021 Cerebral Cortex 18

Forms of Memory • • • Explicit memory Implicit memory Short-term memory Working memory Long term memory 2/26/2021 Cerebral Cortex 19

Explicit Memory • Also called declarative and recognition memory. • It is associated with consciousness or at least awareness. • Events [episodic], rules, words and language [semantic] • Dependant on hippocampus and parts of temporal lobe. 2/26/2021 Cerebral Cortex 20

Implicit Memory • Does not involve awareness • Also called nondeclarative or reflexive memory. • Includes skills, habits, and conditioned reflexes. • It does not involve hippocampus. • Explicit memory can become implicit once it is learnt thoroughly. 2/26/2021 Cerebral Cortex 21

Short-term Memory • Lasts for seconds to hours during which processing in hippocampus or elsewhere lays down long term memory. • Memory traces are subject to disruption by trauma and drugs. • Working memory is a form of short term memory. • It keeps information for very short periods while the individual plans actions on it. 2/26/2021 Cerebral Cortex 22

Long term Memory • Involves changes in synaptic strength. • Stores memories for years or sometimes for life. • Memory traces are remarkably resistant to disruption. • Involves protein systhesis. • Importance of good nutrition for good learning and memory. 2/26/2021 Cerebral Cortex 23

Basis of Memory. • The key to memory is the strength of selected synapses. • It involves protein synthesis during conversion of short term memory into long term memory. • Protein deficiency is associated with poor memory. 2/26/2021 Cerebral Cortex 24