The Neurobiology of Conscious Intent

Perhaps the seminal component of any clinician’s behavioral repertoire is the ability to understand the conscious motivations and intentions of their clients. This article addresses the work of conscious motivations at the neuroanatomical level.

I seldom address the notion of consciousness-let alone motivations-in this column for a very good reason. Nobody really knows what they are or even if there is a “they.” The literature is confusing, but it hasn’t stopped researchers from speculating on possible neuroanatomical and biochemical substrates that undergird the phenomena. Without a broad consensus about what is being studied, there can be no neurons, let alone molecules, for active experimental consideration. After all these years, researchers have yet to isolate an area of the brain solely devoted to the experience of consciousness. There may be none.

Given the importance of these issues to the mental health professions, I revisit the concept of motivations from time to time-but only when the data are conservatively presented, with sober, modest conclusions. The findings described here originate from experiments that have attempted to determine how we voluntarily choose to perform a motor task (action planning). This work requires reviewing background information on association cortices and the neural substrates behind a decision to initiate voluntary action.

Association cortices

Functionally, the cortical regions of the brain and their myriad interlocking circuits can be divided into 3 modules. These consist of front-, back-, and middle-end domains.

• Front-end functional domains are sensory information processing centers. The brain receives input from the eyes, ears, and other sensory systems. It sends the input off to various places for further processing.

• Back-end functional domains involve motor control systems. These systems essentially respond to whatever command the sensory cortices give to it (eg, execute a decision to move).

• The middle-end suite involves nearly everything other than front-end and back-end functional domains. These association cortices generally entail higher processing features and are some of the least understood and the most mysterious parts of the brain.

One such cortex, located in the inferior posterior parietal cortex, is a sensorimotor association region that links sensory stimuli to motor movement. It may even be involved in sensory prediction, which calculates the consequences of a given action through the simultaneous evaluation of input from both sensory (front-end) and motor (back-end) functional domains.

Volitional motor movement

Many of the actions humans initiate on a day-to-day basis seem to depend on a kind of internal free will. This sequence of events (also known as volitional motor movement) gives humans a sense of control: we act because we want to act. That is why researchers use volitional motor movements in their research designs. Researchers interested in volitional behavior study neural prime movers behind decision making.

Exactly what does it mean to want to do something? We do not really know. The events that initiate movement occur in a fairly straightforward sequence (although it depends on the source of the signal). For example, a central processing area with directives for voluntary motor movements pass through a final staging area before the execution of an action. This region is the primary motor cortex.

Research on laboratory animals demonstrates that this cortex decides on a course of action that depends on the source of signals it receives before the execution of that action. One source originates in the premotor cortex. Signals in this area initi-ate movements in response to a specific external trigger, such as a visual cue.

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