|Luria divided the cortex into two functional units. The first,
the posterior portion of the cortex, is the sensory unit.
It receives sensory impressions, processes them, and stores them as information.
The second, the anterior cortex (the frontal lobe), is the motor unit.
It formulates intentions, organizes them into programs of action, and executes
the programs. In both cortical units there is a hierarchical structure,
with three cortical zones arranged functionally one above the other:
the primary cortex, the secondary cortex, and the tertiary
Luria conceived of the cortex as working in the following way. Sensory input enters the primary sensory zones, is elaborated in the secondary zones, and is integrated in the tertiary zones of the sensory, or posterior, unit. For an action to be executed, activity from the posterior tertiary sensory zones is sent to the tertiary zone of the motor, or frontal, unit; where intentions are formed, to the secondary zone where plans of action are formed, and finally to the primary motor zone, where execution of the plans is initiated.
To give a very simplified example of how Luria's model of the cortex might function, say one were walking along and came upon a soccer game. In the primary visual area the actual perception of the movements of people and the ball would occur. In the secondary sensory zone, recognition that those activities constituted a soccer game would occur. In the tertiary zone the sounds and movements of the game would be synthesized into the realization that one team had scored and was ahead and that the game had a certain significance for league standings. This information would be passed on to the paralimbic cortex for processing as a memory and also passed on to the amygdala, where its emotional value would be assessed. These cortical events could then lead, in the tertiary zone of the frontal (motor) cortex, to formation of the intention or plan to play soccer. The programs to execute such a plan would be formulated in the secondary frontal zones. The actual movements to play the game would be initiated in the primary zone of the frontal cortex.
Using the example of a soccer game, we can also describe the effects of brain lesions. A lesion in the primary visual area would produce a blind spot in some part of the visual field, requiring the person to move his or her head backward and forward to see the entire game. A lesion in the secondary area might produce a perceptual deficit, making the person unable to recognize the activity as a soccer game. A lesion in the tertiary area might make it impossible to recognize the significance of the game in its abstract form; that is, that one team wins. Damage to the paralimbic cortex would leave no memory of the event, and damage to the amygdala would leave the person unresponsive to the event's significance. A lesion in the tertiary frontal area might prevent the formation of the intention to become a soccer player and join a club, buy a uniform, or get to practice on time. A lesion in the secondary frontal zone might make it difficult to execute the sequences of movements required in play. Finally, a lesion in the primary zone might make it difficult to execute the discrete movements required in the game; for example, kicking the ball.
Based on: Kolb, B & Whishaw, I.Q. (1996) Fundamentals of Human Neuropsychology, W. H. Freeman, New York pages 169-170.