The three principal functional units in the working brain: An introduction to neuropsychology

Luria, A.R. (1973). The three principal functional units in the working brain: An introduction to neuropsychology (p. 43-101). New York, NY: Basic Books Inc.

In this classic text, Luria describes three principal functional units of the brain whose participation is necessary for mental activity. Each unit has a hierarchical structure consisting of at least three cortical zones: the primary area receiving or sending impulses to the periphery, the secondary area where information is processed or programmed, and the tertiary area involving overlapping zones.

The first functional unit is for regulating tone and waking and mental states and involves the reticular activating formation. This system maintains the optimal level of cortical tone for engaging in organized, goal-directed activity. Processes of excitation obey a law of strength whereby stronger responses are evoked by strong stimuli. Excitation in this system spreads gradually leading to modulation of the entire nervous system. Activation may occur in response to metabolic responses of the organism (e.g., feelings of hunger), stimuli from the outside word leading to an orienting reflex, or to intentions and plans.

The second functional unit is for receiving, analyzing, and storing information, and involves the lateral regions of the neocortex including the visual, auditory, and general sensory regions. The systems of this unit analyze very large numbers of very small component elements, and respond to dynamic functional structures of these stimuli. This system has high modal specificity with component parts adapted to visual, auditory, vestibular, or general sensory information. Associative neurons occurring in the secondary area have less modal specificity, and allow for responding to complex patterns. The tertiary area is a zone of overlapping cortical end of the various analyzers, and allows for the integration of excitation arriving from difference analyzers.

The third functional unit is for programming, regulation, and verification of activity, and largely involves the frontal lobes. This system allows for the creation of intentions, plans, and programming of action, regulating of behaviour, and verifying conscious activity.

The neuropsychological evidence for these three integrated systems provides an evidence base for clinical approaches that consider both the more modality-specific tasks of auditory, phonological, and linguistic learning, and the domain-general executive functions supporting planning and regulating behaviour.

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