The following points highlight the four main lobes of cerebral cortex. The lobes are: 1. Frontal Lobe 2. Parietal Lobe 3. Occipital Lobe 4. Temporal Lobe.
1. Frontal Lobe:
It has area 4, 6—motor and premotor area, 4S suppressor area, 8-frontal eye field. In prefrontal lobe, areas 9-12 are present. Areas 44, 45 are called Broca’s area of speech and this area is present in dominant/categorical hemisphere only (Fig. 9.60).
i. It gives origin to pyramidal tract which is necessary for all voluntary movement and also for skilled movements. Area no. 8 function is essential for accommodation for near vision.
ii. About 40% of communication between individuals is verbal. Areas 44 and 45 have role to play for verbal communication. When these areas are damaged person cannot talk but can understand spoken language.
2. Parietal Lobe:
It has areas 3, 1, 2 termed primary sensory areas and areas 5, 7 called association areas (Fig. 9.61). In primary sensory areas, body representation is contralateral, upside down and extent of representation of body is not dependent on anatomical size of body but on functional importance.
Functions (Fig. 9.62):
i. Function of primary sensory area is to help perception of all general sensations. In addition to this, areas also help in perception of taste sensation.
ii. Association areas help in analysis of all generation sensations and taste sensation.
iii. Areas 3, 1 and 2 also contribute for formation of pyramidal tract that is involved in voluntary movements.
3. Occipital Lobe:
It has areas 17, 18 and 19. Area no. 17 is termed primary visual area and 18 and 19 are called as visual association areas. Fovea centralis part of retina has wider area of representation and relay in occipital lobe of opposite side also. Hence fovea centralis has bilateral representation.
Area no. 17 helps in perception of visual sensation. Areas 18 and 19 help for analysis of vision that is perceived. If there is lesion in occipital lobe of one side, it leads to homonymous hemianopia that is loss of nasal field of vision in one eye and temporal field of vision in opposite eye. In certain homonymous hemianopia, macular sparing may occur due to bilateral representation of macula lutea (fovea centralis).
4. Temporal Lobe:
The lobe has areas 41, 42 which are termed as primary auditory areas and also areas 21 and 22 called auditory association areas. In posterior part of superior temporal gyrus, one more area is present and this is called Wernicke’s area. Wernicke’s area is the general association area and is present in dominant (categorical) hemisphere only.
i. Areas 41 and 42 help for perception of sounds heard and areas 21 and 22 for analyzing details of sound and give meaning for the sound.
ii. Impulses from sensory (general) area, visual (general) area, and auditory (general) area reach Wernicke’s area (Fig. 9.63). When there is damage to this part, person in unable to understand spoken and written language and leads to sensory aphasia. Person can talk but cannot comprehend language (spoken or written).
Functions of Prefrontal Lobe:
1. It has role in learning and memory
2. It is important to maintain moral sense and appropriate social behavior.
3. It has important role to play for balanced emotional reactions.
Functions were studied only after damaging that is after prefrontal lobotomy.
Features of Prefrontal Lobotomy:
1. Flights of ideas:
i. No correlation between statements and action
ii. Random thoughts
i. False sense of well-being prevails
ii. Feeling of conquering world
3. Memory impairment:
4. Alterations in social behavior:
i. For examples, act friendly to snakes
ii. Act unfriendly with humans
5. Lack of initiative:
i. No urge or attempt to bring about activities
ii. No interest to perform certain tasks
iii. Laid back attitude, i.e. lethargy
i. No restraint on emotions
ii. May demonstrate temper tantrums
iii. Balanced emotional reactions are lost
7. Loss of orientation of space and time:
i. Unable to comprehend where they are or what time it is.
8. Impairment of moral sense:
i. Keep doing same task with no rhyme or rhythm
ii. Keep doing same task over and over again (repeated performance of same task).
(Pneumonic to remember prefrontal lobe altered functions after prefrontal lobotomy: FEMALE LIP)