Impulsivity, Compulsivity, and Habit: The Role of Orbitofrontal Cortex Revisited

Humans suffering damage to the orbitofrontal cortex (OFC) are often described as impulsive. The most famous example is Phineas Gage, a railway worker, who in 1848 suffered extreme frontal lobe damage when a long iron rod was projected through his skull after an accidental explosion. Gage survived, but was reported to have an extreme change in personality, including increased inappropriate behavior (impulsiveness) [1–2]. People with OFC lesions are more impulsive compared to both normal controls and people with non-OFC frontal cortex damage, as measured by self-report and by cognitive/behavioral tasks [3]. But, how is impulsivity defined and how can it be measured? Impulsivity involves behaviors that are inappropriate for the context, premature, poorly planned and often resulting in adverse consequences. Impulsive behaviors have been described as having three dimensions: 1) an inability to use available information to reflect on the consequences of actions; 2) an inability to forego an immediate small reward in favor of a delayed larger reward; 3) a deficit in suppressing prepotent motor responses [4]. Taken together, these three dimensions of impulsivity reflect an inability to evaluate and subsequently respond flexibly in search of a specific goal or outcome under changing environmental conditions. In this commentary, we reflect on the similarities between impulsive, compulsive and habitual behavior and hypothesize a common neurobiological circuit that depends critically on the function of the OFC.