Frontal System Dysfunction

The frontal lobes are connected with all of the other lobes of the brain, and they receive and send fibers to numerous subcortical structures as well (Fuster, 1997). Control of motor function takes place in the posterior region of the frontal lobes. The anterior region of the frontal lobes (prefrontal cortex) plays a kind of executive regulatory role within the CNS, inhibiting the occurrence of unnecessary or unwanted behaviors. Disruptions of normal inhibitory functions of frontal lobe neuronal networks often will have the interesting effect of releasing previously inhibited behaviors from frontal control. The resultant aberrant conduct of a frontal patient may be due to the freely unregulated functioning of the released brain regions (disinhibition).

Early evidence for a role of the frontal lobes in supporting the ability to inhibit impulsivity came from the 1868 report of a physician on his patient Phineas Gage. Gage, a railway workman, survived an explosion that blasted an iron bar (about four feet long and an inch wide) through his frontal lobes. After he recovered from the accident, Gage's personality changed. He became irascible, impatient, impulsive, unruly, and inappropriate. The damage had mostly been in the orbital frontal region of Gage's frontal lobes (Mesulam, 2000; Stuss & Knight, 2002).

Damage to frontal brain systems occurs in a number of CNS disorders, including stroke, brain tumors, dementing diseases (e.g., Alzheimer's), and head trauma (Lichter & Cummings, 2001). Patients with bilateral frontal disorders often display a pull to nearby objects (e.g., grabbing at doorknobs) as well as a remarkable tendency to imitate the actions of people nearby (echopraxia). The behaviors of a frontal patient appear not to be based on rational decisions; rather, some responses are under the control of salient objects around them (i.e., objects that capture the attention). In other words, the patient's behaviors are environmentally driven rather than personally chosen. Such behaviors may extend to otherwise embarrassing gestures such as urinating in public or chewing paper.

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