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Read this article to learn about the Cerebral Cortex: Functional Division of the Cerebral Cortex !
Famous neurophysiologist Sherrington said about the human brain, “This great ravelled knot is the master tissue of human body. Mental activities occur as a function of the brain. The responses that a person shows in course of his interaction with the environment are the functions of the brain”.
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The response of an ‘O’ to a stimulus takes place through three basic structures i.e., the receptors, the C.N.S. (Central Nervous System) and the effectors. The C.N.S. consists of the brain and the spinal cord. The P.N.S. (Peripheral Nervous System) brings sensory information’s to the C.N.S. and conducts motor information’s from the C.N.S.
The cerebral cortex contains about 70 per cent of the neurons of the C.N.S. The cerebral cortex is more developed in human beings compared to other animals. It receives direct or indirect apparent information’s from almost every other area of the brain.
The output of the cerebral cortex is called motor activity. It is also involved in producing thoughts and feelings. In view of this, the cerebral cortex is extraordinarily important and has been the centre of much psychological research. In addition to the cerebral cortex many other brain areas are also concerned with higher mental functions.
Functional Division of the Cerebral Cortex:
The cerebral cortex can be anatomically divided into four lobes.
1. Frontal Lobe/Frontal Cortex:
The frontal lobes can be divided into superior, Middle and Inferior gyri, anatomically. However, functionally the frontal lobes may be divided into motor cortex, premotor cortex and prefrontal associational cortex. The frontal cortex is mostly involved in motor behaviour, expressive language, ability to concentrate and attend, reasoning and thinking and orientation to time, place and person.
The prefrontal cortex has also a complex involvement in the evaluation of sensory information. Lesions of the dorsolateral prefrontal cortex produce apathy, indifference, decreased drive to do any work, psychomotor retardation and decreased attention etc.
2. Motor Cortex:
The motor area is located at the end of the frontal lobe and adjacent to the central fissure. It controls the voluntary movements of various parts of the body like leg, arm, face etc. It is technically known as the precentral area (Broadman’s area, 4).
Premotor Cortex:
It is located in front of the precentral area. It controls complex muscular movements of the body. Each hemisphere is connected with the opposite side of the body. If the motor area of the left hemisphere is damaged or destroyed the right limbs are paralysed and vice versa.
Prefrontal Associational Cortex:
It deals with psychological processes like reasoning and memory. The essential function of these areas is to respond to immediate sense impressions and symbols. Because of these areas we are able to correlate all our present experiences with past experiences and make use of memory and thought processes.
Lesions of the orbito medical frontal cortex lead to withdrawal behaviour, fearful explosiveness, loss of inhibitions mood bring a swing and occasional violent outbursts. Some of the patients appear similar to patients with severe by-polar illness.
Parietal Cortex:
It lies near the central fissure in the back half of the brain. It has somasthetic area. The major structure of the parietal cortex includes the post central gyrus, superior parietal lobule and inferior parietal lobule. The parietal lobes contain the associational cortices for visual, auditory and tactile input and hence deal with the intellectual processing of sensory information.
Lesions of the dominant parietal lobe lead to Gerstmann’s syndrome, which includes agrapnia, calculation difficulties, right-left disorientation and finger agnosia. A person with a right sided parietal stroke may deny that he has a paralysed left arm and he may completely ignore the left side of his body like by not washing it while taking bath.
All the bodily sensations are projected in the parietal lobe. If any area of parietal lobe is damaged a person cannot discriminate between a piece of silk cloth and a sand paper. The sensation of wool, pin prick, mud or clay is projected in the parietal cortex.
3. Temporal Cortex:
The lateral aspect of the temporal lobe has three gyri such as superior, middle and inferior. Language, memory and emotions are the primary functions of the temporal cortex. Lesions of the temporal cortex can lead to symptoms like delusions, hallucinations, mood disturbances which by and large resemble those psychiatrics in their research undertakings.
Lesions in the temporal lobe are caused by stroke, trauma, and tumour. Infections in C.N.S. with herpes virus show a particular prediction towards temporal lobes. Bilateral lesions of temporal lobes lead to dementia.
Lesions of the dominant temporal lobe lead to euphoria, auditory hallucination, delusions, thought disorders, decreased ability to learn new materials and poor verbal comprehension. Dysphoria, irritability, cognitive deficiency, decreased visual and musical ability occurs because of lesions of the non- dominant temporal lobe. Damage to the temporal lobe also leads to deafness.
Epilepsy is a major disease characterised by paroxysmal dysfunction of brain tissue. An epileptic focus may be in any cortical area or even subcortical nuclei. But epilepsy is included under the temporal cortex because complex partial epilepsy is probably the most relevant of the epilepsies in psychiatry. Complex partial epilepsy is the most common forms of epilepsy in adults affecting about three in one thousand persons.
4. Occipetal Cortex:
Like other lobes, the occipetal cortex consists of the superior and inferior occipetal gyri as well as the cuneus and the tin lingual gyri. The shape of the occipetal cortex is irregular and it is located at the back portion of the brain. It is the seat of visual sensation.
Total destruction of the occipetal cortex results in cortical blindness. Other subtle dysfunctions are distortion of images and loss of depth perception. If one part of the occipetal lobe is destroyed or there is a lesion the visual field is impaired and the person will not be able to see half of the object.
The retina which is the crucial organ of the eye is connected with it. Hence if one of the optic nerves is demaged either of the eyes will lose its visual ability. Visual hallucination is also found in patients with occipetal epilepsy. Some of these symptoms may be similar to the symptoms of psychiatric patients. Under such circumstances, the psychiatrist may miss the real cause i.e., neurological disorder of the occipetal lobe and thus there may be mistaken diagnosis.
Clinical considerations of different parts of the human brain
Frontal, parietal and temporal lobes are involved in the reception and production of language. Lesions of Brocais area leave comprehension ‘Unimpaired; but produce a productive aphasia in which the speech is telegraphic and agromatical.
Wernicke’s area is located in the temporal lobe and is involved with the comprehension of speech. Because of lesions of Wernickes area the patient cannot understand the spoken word although he has fluent and coherent speech.
Patients with frontal non-dominant lesions are not able to their non-dominance speech with bend affect. Fair speeches to flat patients with posterior lesions are not able to comprehend the abstractness of another person’s speech.
Limbic System and Its Role in Determining Human Behaviour:
The C.N.S. localization for emotions is called the Limbic system by James Paper (1939). The latest models of the limbic system include the amygdala and septal area. Also many parts of the basal ganglia are connected to the limbic system which explains the simultaneous presence of a movement disorder and an emotional disorder in some patients.
Clinical Considerations:
Important psychological functions like emotions, eating behaviour, sex drive, anger, violence, memory and motivation etc. are associated with various parts of the limbic system. Destruction of both the sides (bilateral) of the amygdala and the temporal lobes produce symptoms like hyper quality and severe docility.
Damage or’ injury of the amygdala and anterior temporal lobes have been clinically correlated with a number of behaviours in human beings and symptoms similar to schizophrenia, mania and depression. It is also urgent to note that brain trauma and presence of abnormal E.E.G.S. are commonly found in violent and aggressive children and prisoners.
Basal Ganglia:
Recent researches suggest that the basal ganglia are involved in certain cerebral disorders including psychosis, depression and dementia.
Clinical Considerations:
Disorders in the basal ganglia are basically neurological and produce disorders of movement, thought processes, emotion and cognition. Besides the neurological symptoms, psychiatric symptoms in schizophrenics are also observed. Untreated schizophrenic patients show a larger number of movement disorders that indicate an involvement of the basal gangalia.
Parkinson’s Disease:
Parkinson’s disease (PD) occurs due to the striatal deficiency of dopamine following neuronal degeneration in the brain. Thus, it primarily occurs due to destruction of the dopaminergic cells in the substantia nigra and degeneration of cells in the ventral segmental area and the locus ceruleus.
This leads to tremer, muscle rigidity, stooped posture etc. Hence Parkinson’s disease is characterized by an insidious onset with slowing of voluntary movement, muscular rigidity and postural abnormality. There is imbalance and lack of coordination of movement. It may be caused by encephalitis, carbon monoxide poisoning or head injury.
Depression is a very common syndrome of Parkinson’s patients. The incidence of depression is between 50 per cent to 90 per cent and is more common in males. Dementia which is a symptom of schizophrenia is present in 30 per cent to 80 per cent of the Parkinson’s disease patients.
Basic for the treatment of this disease besides the other, techniques, one latest therapy developed by scientists of U.K. is called ‘Active therapy.’ This revolutionary technique used Medtronic’s brain Pace maker technology to relieve the slowness, stiffness and shaking of the Parkinson’s patients. Activa therapy can also reduce the duration of dyskinesia, the abnormal involuntary movements that are common side effects of medication for this disease.
Activa therapy is highly flexible. In this therapy carefully controlled pulses with minimum side effects of electrical stimulation is given to certain specific areas of the brain. This medical device is similar to a cardiac pace maker.
This is a very effective new approach to treat the disease, says Dr. Rupam Borgehain, a professor at the Neurology Dcptt, Nizam’s Indian Institute of Medical Science. According to him Activa therapy is a major breakthrough in the treatment of Parkinson’s disease up until this point, patients relied on medications that may not provide control of symptoms and also may produce significant side effects On the other hand Activa therapy is highly flexible.
Significant symptom relief can be provided by this technique with minimum side effects. Therapy is reversible i.e., patients can pursue new treatments that may be developed in future.
Huntington’s Disease:
This disease is characterized by dominant movement disorder, deteriorating course of chorea, depression, suicidal tendency, forgetting and psychosis. Psychosis is observed in about 20 per cent of the cases. A recent development of neuropsychiatry is the application of molecular genetics techniques to Huntington’s disease. Wilson’s disease and Fahr’s Syndrome are also observed because of disorders and injuries in the brain.
Hypothalamus and Pituitary:
“The hypothalamus and the Pituitary comprise the master endocrine gland. Thus these two functions as a major integrating and output system for the entire C.N.S.” The hypothalamus not only regulates the endocrine secretion, it is also considered a part of the limbic system and it deals with appetite and sexual regulation.
The hypothalamus and the endocrine system provide special interest to the psychiatrists because of their clinical considerations. Observations indicate that various endocrine disorders have psychiatric symptoms and similarly many psychiatric disorders have endocrine dysfunctions.
According to Kaplan and Sadok, the hypothalamus appears also to have a major role in the centers of biological rhythm and immune system regulation.
Clinical Considerations:
The hypothalamus and pituitary help in the regulation of the endocrine and autonomic nervous system (A.N.S.) and in the control of body temperature, eating behaviour, and sleep wake cycle. The involvement of the hypothalamus in the A.N.S. involved it in psychosomatic disorders.
Destruction of the ventromedial hypothalamus results in hyper-phragia and obesity. Destruction of lateral hypothalamus leads to anorexia and starvation. The limbic system and the prefrontal cortex are also involved in eating behaviour.
The Thalamus and Its Clinical Considerations:
The thalamus has a critical role in the perception of pain. Tumours or vascular lesions of the thalamus can produce severe pain symptoms.
Clinical Considerations Relating to Reticular Activating System:
The reticular activating system is a closely organised network of neurons running up the midline of the brainstem. These neurons receive information’s from the ascending sensory neurons; cerebellum, basal ganglia, hypothalamus and cerebral cortex and send projections to the hypothalamus and spinal cord.
Stimulation of the reticular activating system activates the cortex into a state of alert wakefulness. Disorder and pathology in this area lead to psychiatric disorders involving deterioration and impairment of drive motivational level and level of arousal.
Brain imaging techniques like Magnetic Resonance (M.R.) computed tomography (C.T.) have helped psychiatrists in their investigations and research in the area of clinical psychology.