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UNIT 7 - Cerebral Cortex

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A. Structure
B. Functional Organization

The cerebral cortex developmentally and functionally presents four major divisions:  the Archicortex, the Paleocortex, the Neocortex, and the Cingulate Cortex. The archicortex is involved with emotion and affective behavior regarding visceral activity and is located in the medial aspect of the temporal lobe and includes the hippocampus and dentate gyrus. The cingulate cortex is involved primarily with emotional and affective behavior regarding our three basic drives for food, shelter, and sex. It is located along the inferior, medial aspect of the frontal and parietal lobes.   The paleocortex plays a role in olfaction and is situated along the inferior medial aspect of the temporal lobe and the inferior lateral aspect of frontal lobe. These areas include the parahippocampus, uncus and enthorhinal area within the temporal lobe and orbital gyrus of the frontal lobe. These three divisions are an important part of the limbic system.   Phylogenetically, the neocortex, the remaining portion (90%) of the cortex increases in importance in the ascending vertebrate scale with greatest development seen in man.   It is upon this division that the emphasis of this unit is placed.

A. Structure

The cerebral cortex consists of six cellular layers labeled from superficial to deep as  (1) molecular,  (2) outter granular,  (3) outter pyramidal,  (4) inner granular,  (5) inner pyramidal, and  (6) polymorphic, or fusiform.   All six layers are present throughout the cortex, but vary in depth according to the function of that area of the cortex.   Layers  (1) and  (2) are responsible for receiving information, layers  (3) and  (4) for integrating information, and layers  (5) and  (6) for sending out efferent responses.

B. Functional Organization

Functional divisions of the neocortex are based upon Brodmann's cytoarchitectural map of the cerebral cortex.   Brodmann identified 57 individual areas which he found to differ from a cellular aspect.   Following the development of Brodmann's map of the cerebral cortex, ablation and stimulation studies along with autopsy studies were used to allocate functions to each of these areas.   Verification of these functional areas has been done through computer topography based on electrical, physiological, and blood flow recordings, as well as CAT scans, MRI’s and PET scan studies.

Areas primarily involved with afferent projections from specific thalamic nuclei are referred to as Specific Sensory/Receiving Areas, and areas involved with efferent projections descending to lower motor neurons are called Specific Motor/Sending Areas. Those areas comprising the largest portion of the cerebral cortex, responsible for assessing and giving meaning to sensory stimuli as well as storing information to compare past with present experiences are referred to as Association areas and includes the components of the limbic system.

NOTE: Although many of the precise functional roles of these subdivisions remain in question, those which are generally accepted are described below. In actuality, Brodmann's areas are not as strictly defined as it may appear, and there is considerable overlapping present.

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1. Specific Sensory Areas

The parietal, occipital, and temporal lobes each have a role in the processing of sensory modalities (receiving areas).

a. Primary Somesthetic Cortex - Areas 1,2,3

Location	The post-central gyrus
Function	A receiving area for extroceptive, proprioceptive (concious) and vibratory stimulie from the contralateral side of the body and sends this information to areas 5-7 for integration. This area is broken down according to the body areas called a homunculus and is dipproportionate in nature. The size of the certical representation is determined by functional importance of that area of the body..
Input	Information from the ventral posterior nuclei of the thalamus (VPL and VPM).

Fig. 1 –

The Nervous System, Psychology 9A Lecture 2 Notes, http://hypatia.ss.uci.edu/psych9a/lectures/lec2notes.html

Fig. 2 –

The Nervous System, Psychology 9A Lecture 2 Notes, http://hypatia.ss.uci.edu/psych9a/lectures/lec2notes.html

Fig. 3 –

http://www.geocities.com/HotSprings/3468/9/lobes2.gif
Physiology Of The Human Body, 1985, 3rd Edition, by: J. Robert McClintic, Ph.D.

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b. Primary Visual Cortex - Area 17

Location	The calcarine cortex of the occipital lobe
Function	The primary receiving area for visual information and sends this information to area 18 for interpretation
Input	Receives lateral geniculo-calcarine fibers (optic radiations) and information regarding the contralateral visual field

c. Primary Auditory Cortex - Areas 41,42

Location	The superior temporal gyrus
Function	The primary receiving area for auditory information (verbal and non-verbal) which relays this information to poserior 22 and the planum temporale
Input	Receives medial geniculo-temporal fibers (auditory radiations) which are "tonotrophically localized" receiving input from both cochlea (80% from contralateral ear and 20% from ipsilateral ear.

d.   Primary Gustatory Cortex - Area 43

Location	Along the lateral fissure in the parietal lobe, lateral to the insular cortex just below areas 1-2-3.
Function	The primary receiving area for the sensation of taste and sends this information to areas 5-7 for interpretation
Input	Receives information from the VM, nucleus of the thalamus

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2. Specific Motor Areas

Specific Motor Areas, concerned with initiation of a variety of motor expressions, are primarily located anterior to the central sulcus in the frontal lobe.

a. Primary Motor Cortex - Area 4

Location	The precentral gyrus
Function	Primarily responsible for the control over skeletal musculature for functional activities and mobility skills, via the reticulospinal and corticospinal tracts.  It is also responsible for control of cranial nerve activity via the corticobulbar and reticulobulbar tracts.
Input	Receives information primarily from the ipsilateral ventral lateral and ventral anterior nuclei of the thalamus as well as Areas 1-2-3 (Primary somesthetic cortex) 6,8, and 19, ipsilateral corpus striatum and contralateral cerebellum cortex.

b. Pre-Motor and Supplemental Motor Cortex (Area 6)

Location	Lies in front of the primary motor area. Laterally this area is called the Pre-motor Cortex, medially it is called the Supplemental Motor Cortex (SMC).
Function	The Pre-motor Cortex controls skeletal musculature to provide background postural stability for functional activities and mobility skills via the reticulospinal tracts.  The SMC, is responsible for our motor planning skills.
Input	Receives information from the ipsilateral ventral lateral and ventral anterior nuclei of the thalamus, the inferior olivary nucleus, and Areas 4, 1-2-3, 8, 19 and non-dominate temporal and parietal lobes  (areas 37-39-40), ipsilateral corpus striatum and contralateral cerebellar cortex.

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c. Frontal Eye Fields - Area 8

Location	Found just rostral to the pre-motor area
Function	Information concerned with conjugate voluntary eye movements and pupillary change via corticobulbar tract.
Input	Receives information primarily from the ipsilateral geniculate body, Areas 4, 6, 19, the superior colliculi, and the VA-AL nuclei of the thalamus, corpus striatum and contralateral cerebellar cortex.

d.   Areas 44, 45

Location	Located in the inferior frontal gyrus.
Function	Responsible for innervation of the musculature for speech (the larynx, tongue and lips) on the dominate hemisphere known as Broca’s Speach area.  On the non-dominate hemisphere, these areas deal with reflexive speech.
Input	In the dominant hemisphere receives information from Area 40 on the dominant hemisphere, and the pre frontal cortex (9-10-11-12). On the non-dominant hemisphere information is also received from areas 19, 41, 42, 43 and 1-2-3.

3. Association Areas

These areas are important in regard to the various levels of our cognitive skills

a. Somesthetic Association Cortex - Areas 5, 7

Location	Lies posterior to the post-central gyrus in the parietal lobe (posterior parietal lobule).
Function	Integrates extroceptive, vibratory and gustatory stimulie along with conscious proprioception. (Identifies - Assesses - Stores) (gives meaning to it)
Input	Receives input primarily from Areas 1, 2, 3, and 43.

b. Pre Frontal Area - Areas 9, 10, 11, 12

Location	Located in the anterior portion of the superior, inferior, and middle gyri of the frontal lobe.
Function	Receives input from a variety of cortical areas especially association areas of the cortex as well as projections from the medial nucleus of the thalamus.   Gives total comprehension to all that happens to us.   Responsible for foresight, judgement, abstract thinking, as well as our moods and emotions which make up our personality.

c. Visual Association Areas - Areas 18, 19

Location	Rostral and caudal to the Primary Visual Cortex (Area 17) in the occipital lobe.
Function	Area 18:  Identifies - assesses - stores incoming visual information (Gives meaning to it). Area 19:  Provides visual feedback to Area 4, 6, 8, the superior colliculi, cerebellum, non dominate 37-39-40-44-45 and dominate 39.

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d. Auditory Association Areas - Posterior portion of Area 22 and the Planum Temporale

Location

Posterior 22 is located posterior and caudal to the primary auditory cortex and inferior to the lateral sulcus.   The Planum Temporale is located on the lateral aspect of the temporal lobe, posterior to Areas 41, 42.   In the dominant hemisphere these areas are known as Wernicke's Area.

Function

Identifies - assesses - and stores non-verbal auditory information (gives meaning to it) but does not interpret verbal input which must be sent to area 40 in the dominant hemisphere for interpretation. However, only these areas on the dominant hemisphere known as Wernicke's Area can relay verbal input to area 40 on the dominant hemisphere for interpretation. damage to these areas results in no verbal input being sent to area 40.

e. Supramarginal Gyrus - Area 40

Location	Anterior inferior parietal lobule.
Function	Interprets and stores information dealing with the spoken word in dominate hemisphere.   In non-dominate hemisphere, this area is responsible for our perceptual skills (visual-spatial-temporal).  Area 40 in the dominate hemisphere receives verbal input from Posterior 22 and planum temporale (Wernicke’s Area).  In the non-dominate hemisphere information is received primarily from areas 5-7, 19, areas 39- 40 of the dominate hemisphere and vestibular input from the vestibular receiving area.
Output	Information from the dominant hemisphere is shared with area 9-10-11-12 and sent to areas 44-45 on the dominant hemisphere (Brocca's Area) to formulate a verbal response. Information from the non-dominant hemisphere is sent primarily to areas 9-10-11-12, 4, 6, 8, corpus striatum and cerebellum.

f. Angular Gyrus - Area 39

Location

Posterior inferior parietal lobule.

Function

Interprets and stores information dealing with the written word in dominate  hemisphere.  This area is responsible for our perceptual skills (visual-spatial-temporal) in the non-dominant hemisphere.  The dominate hemisphere receives information primarily from area 19.  In the non-dominant hemisphere, it receives information primarily from areas 5-7, 19, and areas 39-40 of the dominate hemisphere and vestibular input from the vestibular receiving area. Output is as listed from area 40.

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Frontal/Parietal/Temporal Lobe -- Dominant vs. Non-Dominant Areas: 21, Anterior 22, 37, 39, 40, 44, 45

a. Dominant

Function - Areas 37, 39, 40, 44, and 45 are responsible for our communication skills, such as our ability to understand the written and spoken word, and our ability to speak, write, and to communicate in other manners such as sign language.

Area 21 and anterior 22 deal with our ability to solve problems through calculations and basic analytical skills.

Area 21 and anterior 22 are also responsible for certain perceptual skills, which include distinguishing right from left, depth perception, recognizing, and distinguishing between fingers.

b. Non-dominant

Function - Areas 37, 39, and 40 provide for our basic perceptual skills, which are visual, spatial, and temporal skills. They allow us to organize our environment in space and time.   They give us the ability to distinguish between right and left, up and down, in and out, forward and backward, and vertical from horizontal.   These areas also allow us to distinguish foreground from background including depth perception, to recognize differences between various shapes and forms, and to recognize faces and signs.  These skills allow us to orient ourselves to our environment, follow directions, and plan appropriately for motor activities.   In addition these areas allow for the perception of the significance of time.

Area 21 and anterior 22 deal with our creativity and artistic skills.   These being our ability to draw, paint, sculpt, compose music, poetry, written word, general musical talents, and the general ability to create, or be creative (decorate rooms, coordinate colors, plan construction).

Areas 39, 40, 44, and 45 deal with reflexive speech such as (phrases like Hi, Goodbye, Good morning, slang expressions, songs, poetry, song lyrics or verses put to memory, etc.) This area also deals with gesturing as a manner of communication.

In addition, Areas 21, anterior 22, 37, 39, 40, plus Areas 5, 7,18, posterior 22 and the planum temporale in both hemispheres allow for total conceptualization of what one is experiencing at that moment in time by totally integrating all sensory input.

Fig. 4 –

Fig. 5 –

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