Cerebral Cortex

Abstract

The cerebral cortex is a telencephalic structure present in some vertebrate species located at the surface of the cerebral hemispheres. It is the brain area most recently acquired in evolution. The cerebral cortex resembles a six layer sheet of neurons that in many animals, including humans, is folded to fit into the confines of the skull. Each cerebral cortex hemisphere is made of four anatomically distinct lobes: frontal, parietal, occipital and temporal. Within these lobes, different cortical functions are carried out by functionally and anatomically distinct cortical areas. Although structurally similar, the two hemispheres of the cortex are not functionally equivalent. The cerebral cortex is involved in many higher‐level functions such as sensory perception, cognition, language, memory, decision making, motor planning and control.

Key Concepts

  • The cerebral cortex is well‐organised anatomical structure with six neuronal layers and subareas that are anatomically and functionally distinct.

  • The cerebral cortex is composed of different neuronal subtypes that are organised into networks that connect neurons within and between distinct functional areas.

  • A large part of the cerebral cortex is devoted to processing sensory stimuli from the environment.

  • The remainder of the cortex is devoted to motor planning and control, as well as integration of multiple sensory cues and cognitive processing.

  • The two hemispheres of the brain are similar in organisation but distinct in some functions.

  • The complex networks of the cerebral cortex are specified in development using intrinsic molecular cues and spontaneous neuronal activity, although sensory‐driven activity can also play a role.

Keywords: sensory; motor; association; lateralisation; cortical column; cognition

Figure 1. The structure of the cerebral cortex. The human cerebral cortex is made up of distinct functional areas. Sensory cortices (visual, auditory and somatosensory) process information received from peripheral sense organs, motor areas plan and instruct motor output and association areas integrate cortical inputs to create meaningful motor outputs and cognitive and emotional constructs.
Figure 2. Cells and circuitry of the cerebral cortex. (a) Image showing the morphology of several cortical neurons and their dendrites (A – dendrites of the apical tuft; B – basal dendrites). Neurons were stained using the Golgi technique. (b) Reconstructions of Golgi‐stained neurons. Top panel: layer 3 pyramidal neuron. Lower panel: layer 4 spiny stellate neuron. Notice the very different dendritic morphology between these two classes of cells. (Photo and camera lucida drawing by Grazyna Gorny, provided by Terry Robinson.) (c) Cortical microglia stained with an antibody against Iba‐1. (d) Cortical astrocytes stained with an antibody against glial fibrillary acidic protein (GFAP). (Image provided by Maiken Nedergaard.)
Figure 3. Circuitry of the cerebral cortex. Neurons in different layers have stereotyped projections including feedforward, feedback and lateral connections. Neurons with similar properties are arranged in a columnar manner suggesting that single columns containing canonical circuits may be the basic unit of processing in the cerebral cortex.
Figure 4. The sensory and motor homunculi. A homunculus is a little person represented in the motor (a) and somatosensory (b) cortex delineating the amount and location of cortical space devoted to sensing or moving the appropriate body part. The representation is distorted such that areas that require fine motor control or that provide a lot of information about the sensory world (such as fingers) occupy a relatively larger cortical space. Notice that while the motor and sensory homunculi are similar, they are not identical (This figure is redrawn from Penfield and Rasmussen, ).
Figure 5. Hemispatial neglect. (a) An example of a test used to assess spatial neglect. A patient was asked to mark the midpoint of lines of various lengths. Patients with hemispatial neglect tend to deviate away from the true midpoint and occasionally omit lines on their neglected side (left) altogether. (Adapted from Vuilleumier P., © John Wiley & Sons Ltd.) (b) An example of a Gainotti test, a classic test used to assess hemispatial neglect. The patient is asked to copy a picture (top panel) containing five objects. The patient usually fails to draw the objects located in the neglected hemifield (lower panel). (Adapted from Rossetti et al., 1998 © Nature Publishing Group.)
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Further Reading

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Majewska, Ania K(Jan 2015) Cerebral Cortex. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000090.pub2]