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 1200cm3
• 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

18. Frontal lobe
Subdivided into
• Precentral cortex
• Prefrontal cortex

19. 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

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

21. 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”

22. 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

23. 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

24. 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

25. 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

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

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

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

29. 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

30. 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

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

32. 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

33. 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

34. 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

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

36. Thank you