Broca's Area and the Hierarchical Organization of Human Behavior

Abstract

The prefrontal cortex subserves executive control, i.e., the organization of action or thought in relation to internal goals. This brain region hosts a system of executive processes extending from premotor to the most anterior prefrontal regions that governs the temporal organization of behavior. Little is known, however, about the prefrontal executive system involved in the hierarchical organization of behavior. Here, we show using magnetic resonance imaging in humans that the posterior portion of the prefrontal cortex, including Broca's area and its homolog in the right hemisphere, contains a system of executive processes that control start and end states and the nesting of functional segments that combine in hierarchically organized action plans. Our results indicate that Broca's area and its right homolog process hierarchically structured behaviors regardless of their temporal organization, suggesting a fundamental segregation between prefrontal executive systems involved in the hierarchical and temporal organization of goal-directed behaviors.

Neural evidence for the interplay between language, gesture, and action: A review

“…Several studies indicate however that inferior frontal cortex is also recruited for other purposes, such as action observation, sequencing or semantic selection (e.g. Koechlin & Jubault, 2006;Molnar-Szakacs, Iacoboni, Koski, & Mazziotta, 2005;Thompson-Schill, D'Esposito, Aguirre, & Farah, 1997). There are two ways to explain the multitude of conditions that make inferior frontal cortex 'light up'.…”

“…Thompson-Schill and colleagues, for instance, suggest that the inferior frontal cortex is involved in 'the regulation of mental activity ' (Thompson-Schill, Bedny, & Goldberg, 2005). Hierarchical processing is another suggested overarching function of the inferior frontal cortex (Koechlin & Jubault, 2006;Tettamanti & Weniger, 2006;see Friederici, 2006;van Schie, Toni, & Bekkering, 2006 for related accounts). However, another way of conceiving the broad range of tasks activating inferior frontal cortex is to think of an area as a node in multiple different networks, in which the network and not the area instantiates a function (Fuster, 2003;Mesulam, 1990Mesulam, , 1998.…”

Two principles of organization in the prefrontal cortex are cognitive hierarchy and degree of automaticity

“…T he lateral prefrontal cortex (PFC) has been segregated into subregions based on several functional characterizations [1][2][3][4] . Specifically, the 'cascade model', focusing on the temporal context, describes how executive function can be fractionated into hierarchically ordered control processes, each responsible for selecting an action based on temporal framing 5 .…”

“…From this temporal dimension, one can distinguish three major cognitive control processes with increasing levels of hierarchy: contextual control (CONT) for making stimulus-response associations in the immediate context, episodic control (EPIS) for responding to stimuli depending on discrete past events, and branching control (BRAN) for selecting subsequent actions based on information conveyed by past events while intervening actions occur. The left PFC has been described as forming a cascade of subregions along the posterior-to-anterior axis based on the three levels of cognitive control: the posterior PFC (Brodmann area (BA) 44) for CONT, representing the lowest level of hierarchy; the more anterior PFC (BA 45) for EPIS, representing a mid-level of hierarchy; and the most anterior frontopolar cortex (BA 10) for BRAN, representing the highest level of hierarchy [4][5][6] . Similar to cognitive control, cross-temporal contingencies are a pivotal factor in natural language processing.…”

“…Studies in the nonlanguage (NL) domain have reported a functional gradient within the left PFC, based on the hierarchy of cognitive control and operating from the posterior region for the lowest level (CONT) to the anterior region for the highest level (BRAN) 4,6,8,9 . Contrastingly, in the language domain the posterior left PFC (that is, BA 44) has been observed as the 'sensitive' area associated with linguistic hierarchy; as the level of complexity becomes higher, activation in BA 44 increases 10 .…”