Cerebral cortex: functional areas

Dr. Madanmohan. MD, DSc, FIAY

Professor & Head

Department of Physiology

Learning objectives

1. Give the similarities and differences between

brain and computer.

2. State the differences between allocortex and

neocortex.

3. Name the functional areas of different lobes of

brain.

4. Name the components and functions of

prefrontal cortex.

5. Briefly describe the functions of cortical

association areas.

6. List the differences between categorical and

representational hemispheres.

Scheme of talk

• Introduction

• Functional areas of brain

• Association areas of brain

• Complementary specialization

• Methods of study

Introduction

• Highest level of functioning:

intelligence, behavior, perceives,

interprets, stores, responds, regulates.

• 100 billion (1011) neurons

Each neurone has 103 synapses

1011 neurons have 1014 synapses

• Extensive connections, functional overlap

Brain and computer

Common terms: input/output, processing,memory

Computer:

• Faster, more accurate, memory is permanent

• Follows program blindly, no creativity or

abstract thought

• Modern computers have artificial intelligence

Cerebral cortex

Frontal, parietal, temporal, occipital

Limbic system

Hypothalamus

Functional coupling

endo ANS somatic

Pituitary Brain stem

Int. responses (Hs) Ext. responsesContd…

… Contd

Internal responses: External responses:

Metabolism. Behaviour:

Cardiovascular …. Eating, drinking

adjustments.

1. Allocortex / archipallium: 3 cell layers

8%. primitive, heterotypical, limbic

2. Neocortex / neopallium / ioscortex:

6 layers, highly developed in humans

3. Juxtallocortex: transitional cortex,

cingulate, insula

Frontal lobe

1. Primary motor area. 4. Pre-rolandic gyrus

Topographical map, upside down.

Stimulation: movement in opposite half

Lesion: contralateral paralysis

Double lesion: severe paralysis

Movement, execution, behavior

2. Supplementary motor area:

Medial frontal gyrus,

medial surface of hemisphere.

Higher order motor control

Stimulation: threshold is higher

Lesion: temporary paralysis

3. Pre motor area: 6, 8

Stimulus: intricate movements

Lesion: less severe paralysis

Skilled movement lost

Destruction of 4, 6, 8:

severe contralateral paralysis

4. Frontal eye field: 6, 8, 9Connected to visual cortex.

Voluntary scanning movements

Stimulus: conjugate movements of eyes

to opposite side

5. Broca’s motor speech area: 44, 45

Lesion in categorical hemisphere:

expressive aphasia

can understand written or spoken words

6. Micturition center: medial frontal lobe

7. Prefrontal cortex: 9,10,11,12,24,32

Frontal, orbital, medial frontal gyrus.

Extensive area, numerous connections.

Associates somatic and visceral functions.

Functions:

i) Discrimination & judgement

ii) Emotions

iii) Personality

iv) Behavior

Frontal leukotomy /lobectomy:

for intractable pain and stress.

Parietal lobe

Perception, integration

1. Primary sensory (somesthetic) area (SI) 3,1,2

Post central gyrus, upside down.

Orderly representation of opposite ½

Stimulation: sensory experiences.

Lesion: sensory disturbances/loss

more in distal parts

Bilateral lesion: severe loss

2. Secondary somesthetic area: S II

Superior lip of posterior limb of lat. fissure

Body completely represented: face ant.

3. Somesthetic association area: 5, 7

Sup. parietal lobe, supramarginal gyrus

Receives & integrates sensory modalities

Sensory discrimination, i.e., warm from warmer

Lesion: astereognosis. Neglects opp ½ of body

4. Taste: 43 postcentral gyrus

5. Visceral: insula, buried in lateral sulcus

Occipital lobe

1. Primary visual area: 17

2. Secondary visual area: 18

Visual association/psychovisual area.

3. Occipital eye field: 18,19

Sti: conjugate deviation to opposite side

Temporal lobe

1. Primary auditory area: 41, 42

Inferior wall of lateral sulcus

Receives sound from both sides

2. Secondary auditory area: 22

Intepretation of sound.

Lesion:

unable to intepret sound (word deafness).

3. Olfactory area: Limbic system.

Olfactory cortex, ant olfactory nucleus,

pyriform cortex, olfactory tubercle.

4. Taste: 43

Taste area I: near area for tongue

Taste area II: deep in insular cortex

5. Vestibular area: posterior parietal cortex

Afferents: i) vestibular system

ii) visual association area

iii) auditory association area

Bilateral temporal lobectomy

(Kluver – Bucy monkey)

1. Change in emotional state and behavior

2. Change in dietary habits and sexual behavior

3. Docile, distractable

4. Loss of recent memory

Association areas of cortex

• Primary sensory & motor areas: <10 %

• Association areas >90 %

• Immense growth in humans

• Large areas, multiple connections,

complex functions

• Store, integrate, associate, interpret

• Primary motor & sensory aareas: <10%

4 3,1,2 17 41

• Unimodel association areas:

6,8 5,7 18 22

Heteromodel association areas:

Parietal-occipto-temporal: 30, 40……

Language: Computes somatosensory, visual and

auditory information

Pre-frontal (frontal): 9, 10, 45, 46, 47……

Complex, high order functions

Complementary specialisation

Categorical (dominant ?)

Language, sequential analysis

Occipital lobe wider

Lesion: language disorder,

depressed

Representational

Visuospatial, spatio-

temporal, recognize faces,

musical themes

Frontal lobe thicker

Lesion: astereognosis,

euphoric,

unconcerned

Cell layers: 3 in allocortex, 6 in neocortex

1. Molecular (plexiform) layer: outer

2. External granular layer

3. Pyramidal cell layer

4. Internal granular layer

5. Internal pyramidal / ganglionic layer

6. Fusiform cell layer

1.Electrophysiology: normal volunteers

neurosurgery, EEG, EP, stimulation, NC, EMG.

2. Imaging: plain x-ray, CAT, MRI, PET, SPECT,

fMRI.

3.Biochem / molecular: blood, urine, CSF (LP).

4.Clinico-pathological: biopsy, autopsy, denervation,

degeneration.

5.Ablation: animals, patients, stereotaxy.

6.Pharmacological: drugs, neurotransmitters.

7.Embryo transplant.

Methods of study

Thank you...