Cerebral cortex

structure,functons,lesions

1. Cerebral cortex Dr Anu Priya J

2. The adult human brain weighs on average about 1.5 kg with a volume of around 1200cm 3 The cerebral hemispheres form the largest part of the human brain The hemispheres are covered with a cortical layer with a convoluted topography, sulci and gyri

3. Separated from each other in the upper part by a median longitudinal fissure In the lower part, the hemispheres are connected by the corpus callosum

4. Neocortex (Association cortex) Cerebral dominance (Cerebral asymmetry) Lobes of cerebral cortex

5. Neocortex (Association cortex)

6. Neocortex (Association cortex) Phylogenetically newest part of the cortex The seat of all higher functions (not only sensori -motor association but also intellect, language, speech, personality, learning & memory)

7. Functional organization Frontal or Prefrontal association cortex Parietal-occipital-temporal association cortex Temporal association cortex Limbic association cortex

8. Functions of neocortex Language function – dominant hemisphere (categorical hemisphere) Fn of the association cortex located in the temporal region & language areas (mostly left side – Wernicke’s area, Angular gyrus, Frontal motor speech areas) Understand the spoken and written words Express ideas in speech and writing

9. Recognition of faces – non-dominant hemisphere (representational hemisphere) Right inferior temporal lobe – integrate & store information regarding recognition of faces – receive visual input from objects, particularly the visual impression of faces Lesion Prosopagnosia – inability to recognize faces (recognize known people by their voice, but not by seeing their faces) Functions of neocortex

10. Calculation Inferior part of left frontal lobe – actual calculation Areas around the intraparietal sulci – memorizing numbers & finger counting Lesion Acalculia – impairment of mathematical ability Functions of neocortex

11. Navigation Sense of direction-findings Right side hippocampus Right side caudate nucleus Functions of neocortex

12. Histology of neocortex The neocortex is composed of 6 layers I to VI from outside to inside Three types of cells can be identified Pyramidal cells Stellate or granule cells Fusiform cells

13. Cerebral asymmetry (Cerebral dominance)

14. Cerebral asymmetry Dominant – categorical – language, calculation Nondominant – representational – recognise faces, navigation Mostly left hemisphere dominant Not associated with handedness Explain the functions : Refer Neocortex

15. Lobes of the cerebral cortex

16. Lobes Each hemisphere is divided into 4 lobes

17. Frontal lobe Subdivided into Precentral cortex Prefrontal cortex

18. Areas of precentral cortex Primary motor area – Brodmann’s area 44 and 45 Premotor area – Brodmann’s area 6, 8, 4 and 45 Supplementary motor area

19. Prefrontal cortex Also known as orbitofrontal cortex Lies anterior to area 8 and 44

20. Functions Centre for planned actions – plans complex patterns and sequence of motor movements Centre for higher functions – centre for learning, emotions, memory, social behaviour Seat of intelligence - short term memories are stored and recalled. “ Organ of mind”

21. Control of intellectual activities To prognosticate To plan for the future To concentrate on a theme of thought, elaboration of thought Delays actions in response to incoming signal to obtain best response Consideration of consequences of motor action Solution of complicated mathematical and philosophical problems

22. Frontal lobe syndrome Bilateral prefrontal lobectomy Phineas case – rod pierced brain Flight of ideas – difficulty in planning Emotional instability – lack of restraint – hostile,aggressive,restless Impairment of recent memory alone; remote memories intact Loss of moral and social sense Lack of attention & concentration power Lack of initiative – reducing mental drive Functional abnormalities – hyperphagia , loss of control over urinary or rectal sphincters, orientation disturbance, slight tremors

23. Parietal lobe Primary sensory area – Brodmann’s areas 3, 1 and 2  S1 Secondary sensory area  S2 Sensory association area – Brodmann’s area 5 and 7

24. Lesion in primary sensory area S1 When lesion is confined to sensory cortex, sensations are perceived but discriminating functions are lost When thalamus is also involved, there is loss of sensations

25. Secondary sensory area Lesion causes deficits in discrimination power Sensory processing in S1 is preserved

26. Sensory association area Lesion in area 40 produces tactile agnosia - astereognosis and tactile aphasia

27. Temporal lobe Primary auditory cortex (41,42) Auditory association area (20,21,22)

28. Unilateral removal of temporal lobe Does not cause deafness as each ear is bilaterally represented Removal of one auditory cortex has only a slight effect on auditory acuity i.e. sharpness of hearing

29. Temporal lobe syndrome Also known as Kluver-Bucy syndrome Produced experimentally in animals after removal of bilateral temporal lobe along with amygdala and uncus Hyperphagia , omniphagia , increased oral activity, hypersexuality

30. Features of temporal lobe syndrome Aphasia – disturbance in speech Auditory disturbances – tinnitus, auditory hallucinations with sounds like buzzing, ringing or humming

31. Wernicke’s aphasia Comprehension for spoken and written language is impaired Language output is fluent but highly paraphasic and circumlocutious Jargon aphasia – string of neologism Language contains few substantive nouns  speech is voluminous but uninformative 22

32. Occipital lobe Primary visual cortex - area 17 – perception of visual impulses Visual association area – Area 18 and 19 – recognition and identification of objects with past experience Occipital eyefield – Area 19 – movements of eyeball

33. Modified nomenclature of visual areas V1 – first visual area – Area 17 V2 – second visual area – greater part of Area 18 V3 – third visual area – narrow strip of Area 18 V4 – fourth visual area – Area 19 V5 – fifth visual area – posterior end of temporal gyrus

34. Lesion in visual cortex Loss of perception of visual impulses Loss of recognition and identification of known objects

35. Thank you