Functional Areas of Cerebral Cortex

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FUNCTIONAL AREAS OF CEREBRAL CORTEX

  • Cerebral cortex is divided into a number of areas for functional analysis.
  • Frequently referred functional areas are “52 areas of Brodmann”.
  • Cortical areas are divided into-
    • Motor Areas
    • Sensory Areas 
    • Psychical Area



MOTOR AREAS

  • Motor areas occupy Frontal lobe.
  • They are further subdivided into-
    • Primary Motor Area (Area No. 4)
    • Pre-Motor Area (Areas 6 & 8)
    • Supplementary Motor Area
    • Pre-Frontal Area (Areas 9 - 12)

PRIMARY MOTOR AREA (AREA NO. 4)

Location :-

  • Pre-central gyrus & anterior part of paracentral lobule.

Connections :-

Afferents-

  • From ventral nuclei of thalamus.
  • From other cortical areas of same hemisphere through association fibres.
  • From cortical areas of opposite hemisphere through commissural fibres.

Efferents-

  • Cortico-bulbar tract
  • Cortico-nuclear tract
  • Cortico-spinal tract
  • Fronto-pontine fibres
  • Fibres to corpus striatum
  • Fibres to red nucleus
  • Fibres to brain stem
  • Fibres to reticular nuclei

Functions :-

  • Controls voluntary movements of contra-lateral side of the body.
  • Motor homunculus- Centres for movements are represented somatotopically on the motor cortex in inverted position with head end below and leg end up.

PRE-MOTOR AREA (AREAS 6 & 8)

Location :-

Area No.6-

  • It lies in front of area 4 in the posterior parts of superior, middle & inferior frontal gyri.
  • Upper part of area 6 extends on to the medial surface of frontal lobe.
  • Lower part of area 6 extends forward in the inferior frontal gyrus known as Broca’s area (Areas 44 & 45).

Area No.8-

  • It is known as frontal eye field.
  • It lies in front of area 6 in the posterior part of middle frontal gyrus.

Connections :-

Afferents-

  • From ventral nuclei of thalamus

  • From other cortical areas of same hemisphere through association fibres.
  • From cortical areas of opposite hemisphere through commissural fibres.

Efferents-

  • Cortico-bulbar tract
  • Cortico-nuclear tract
  • Cortico-spinal tract

Functions :-

Area No.6-

  • It is concerned with programming or integration of voluntary movements to perform skillful acts.
  • Upper part of area 6 possess a writing centre, concerned with co-ordinated movements of writing.
  • Broca’s area acts as motor speech centre and regulates co-ordinated movements of lips, tongue, palate larynx & pharynx.

Area No.8-

  • It regulates the voluntary conjugate movements of eyes.

SUPPLEMENTARY MOTOR AREA

Location :-

  • Posterior part of medial frontal gyrus and continues with area 6.

Connections :-

Afferents-

  • From ventral anterior and ventral lateral nuclei of thalamus.

Efferents-

  • Project to primary motor cortex (area 4).

Functions :-

  • It controls the complex movements which require sequential organization.

  • It elicits the sensation of an urge to move.

PRE-FRONTAL AREA (AREAS 9 - 12)

Location :-

  • Pre-frontal cortex rostral to the pre-motor area.

  • It is subdivided into areas 9, 10, 11, 12.
  • Area 12 is predominant on the orbital surface of frontal lobe.

Connections :-

Afferents-

  • From dorso-medial nuclei of thalamus.

  • From hypothalamus.
  • From limbic system.
  • From almost all areas of cerebral cortex.

Efferents-

  • Project to dorso-medial nuclei of thalamus, hypothalamus & limbic system.

Functions :-

  • It regulates the depth of feeling of an individual.

  • It is essential for abstract thinking, mature judgement, foresight & tactfulness.
  • Pre-frontal area is called as silent area of the brain since its function is non-specific.


SENSORY AREAS

  • Sensory areas are divided into-
    • Somesthetic / Somato-Sensory Areas
    • Visual Areas
    • Auditory Areas

SOMESTHETIC / SOMATO-SENSORY AREAS

  • Somesthetic areas occupy Parietal lobe.
  • They are further subdivided into-
    • Primary Somesthetic Area (Areas 3, 1, 2)
    • Secondary Somesthetic Area
    • Association Somesthetic Area (Areas 5 & 7)
    • Higher Association Somesthetic Area (Area No. 40)

PRIMARY SOMESTHETIC AREA (AREAS 3, 1, 2)

Location :-

  • Areas 3, 1, 2 are arranged from before backwards in post-central gyrus & posterior part of paracentral lobule.

  • Lower part of the post-central gyrus known as Gustatory area (Area No. 43).

Connections :-

Afferents-

  • From VPM & VPL nuclei of thalamus.

  • From other cortical areas through association fibres.

Efferents-

  • Contribute fibres to cortico-spinal, cortico-bulbar & cortico-nuclear tracts.

  • Fibres to other cortical areas.

Functions :-

  • It localizes, analyses, discriminates cutaneous & proprioceptive senses from contra-lateral side.

  • Area 3 is concerned with cutaneous senses of touch, pressure, position & vibratory senses.
  • Area 1 is concerned with cutaneous & joint senses.
  • Area 2 is concerned with proprioceptive senses from muscles & joints.
  • Upper part of area in the paracentral lobule receives sense of distension from urinary bladder and rectum.
  • Gustatory area acts as taste receptive centre.
  • Sensory homunculus- Areas of sensation are somatotopically represented upside down with head below and leg up on the somesthetic cortex.

SECONDARY SOMESTHETIC AREA

Location :-

  • Lower part of post-central and pre-central gyri along the upper lip of posterior ramus of lateral sulcus.

Connections :-

Afferents-

  • From VPM & VPL nuclei of thalamus.

Efferents-

  • Contribute fibres to cortico-spinal, cortico-bulbar & cortico-nuclear tracts.

Functions :-

  • It receives cutaneous sensations, predominantly pain, from contra-lateral side of the body.

ASSOCIATION SOMESTHETIC AREA (AREAS 5 & 7)

Location :-

  • Superior parietal lobule.

Connections :-

Afferents-

  • From primary somesthetic area (areas 3, 1, 2).

  • From pulvinar end of thalamus.

Efferents-

  • Project to primary somesthetic area & pulvinar end of thalamus.

Functions :-

  • Processing of perception or recognition of general senses.

HIGHER ASSOCIATION SOMESTHETIC AREA (AREA NO. 40)

Location :-

  • Supra-marginal gyrus of inferior parietal lobule.

Connections :-

Afferents-

  • From association somesthetic area (areas 5 & 7).

  • From pulvinar end of thalamus.

Efferents-

  • Project to pulvinar end of thalamus.

Functions :-

  • Processing of perception or recognition of general senses.

 


VISUAL AREAS

  • Visual areas occupy Occipital lobe.
  • They are further subdivided into-
    • Primary Visual Area (Area No. 17)
    • Association Visual Area (Areas 18 & 19)
    • Higher Association Visual Area (Area No. 39)

PRIMARY VISUAL AREA (AREA NO. 17)

Location :-

  • Cuneus & lingual gyrus along the lips & walls of calcarine sulcus.

Connections :-

Afferents-

  • From lateral geniculate body through optic radiation.

  • From association visual area (areas 18 & 19) of same & opposite hemispheres.

Efferents-

  • Project to association visual area (areas 18 & 19) of same & opposite hemispheres.

Functions :-

  • It registers the opposite field of vision.

ASSOCIATION VISUAL AREA (AREAS 18 & 19)

Location :-

  • It surrounds the primary visual area on medial & lateral surfaces of occipital lobe.

  • Areas 18 & 19 together form occipital eye field.

Connections :-

Afferents-

  • From primary visual area (area no. 17).

  • From other cortical areas.
  • From pulvinar part of thalamus.

Efferents-

  • Project to superior colliculus & motor nuclei of extra-ocular muscles through optic radiation.

Functions :-

  • Recognition of objects.

  • Regulate the conjugate movements of eyes.

HIGHER ASSOCIATION VISUAL AREA (AREA NO. 39)

Location :-

  • Angular gyrus of inferior parietal lobule.

Connections :-

Afferents-

  • From association visual area (areas 18 & 19).

Efferents-

  • Project to superior colliculus & motor nuclei of extra-ocular muscles through optic radiation.

Functions :-

  • Processing of visual impression to comprehend the objects & symbols of language.

 


AUDITORY AREAS

  • Auditory areas occupy Temporal lobe.
  • They are further subdivided into-
    • Primary Auditory Area (Area No. 41)
    • Association Auditory Area (Area No. 42)
    • Higher Association Auditory Area (Area No. 22)

PRIMARY AUDITORY AREA (AREA NO. 41)

Location :-

  • Anterior transverse temporal gyrus on the upper surface of superior temporal gyrus.

Connections :-

Afferents-

  • From medial geniculate body through auditory radiation.

Efferents-

  • Project to auditory areas of same & opposite hemispheres.

Functions :-

  • Detection of changes in frequency & direction of sound.

ASSOCIATION AUDITORY AREA (AREA NO. 42)

Location :-

  • Posterior transverse temporal gyrus on the upper surface of superior temporal gyrus.

Connections :-

Afferents-

  • From primary auditory area (area no. 41).

  • From higher association auditory area (area no. 22).

Efferents-

  • Project to auditory areas of same & opposite hemispheres.

Functions :-

  • Recognition of sound.

HIGHER ASSOCIATION AUDITORY AREA (AREA NO. 22)

Location :-

  • Superior temporal gyrus behind the primary & association auditory areas.
  • Area no. 22 is also known as Wernicke’s area.

Connections :-

Afferents-

  • From primary auditory area (area no. 41).

  • From association auditory area (area no. 42).
  • From Broca’s area (areas 44 & 45).

Efferents-

  • Project to Broca’s area through association fibres.

Functions :-

  • Wernicke’s area acts as sensory speech centre.

  • It is concerned with interpretation of sounds & comprehension of spoken language.

 

PSYCHICAL AREA

Location :-

  • Anterior part of temporal lobe including the temporal pole.

Connections :-

Afferents-

  • From limbic system.

Efferents-

  • Project to limbic system.

Functions :-

  • Concerned with hallucination, memory & dreams.

  • Recall of object seen, music heard, experiences in the recent or distant past.

 


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