Hierarchical processing in the prefrontal cortex in a variety of cognitive domains

Abstract

This review scrutinizes several findings on human hierarchical processing within the prefrontal cortex (PFC) in diverse cognitive domains. Converging evidence from previous studies has shown that the PFC, specifically, BA44, may function as the essential region for hierarchical processing across the domains. In language fMRI studies, BA 44 was significantly activated for the hierarchical processing of center-embedded sentences and this pattern of activations was also observed in artificial grammar. The same pattern was observed in the visuo-spatial domain where BA44 was actively involved in the processing of hierarchy for the visual symbol. Musical syntax, which is the rule-based arrangement of musical sets, has also been construed as hierarchical processing as in the language domain such that the activation in BA44 was observed in a chord sequence paradigm. P600 ERP was also engendered during the processing of musical hierarchy. Along with a longstanding idea that a human’s number faculty is developed as a “by-product of language faculty”, BA44 was closely involved in hierarchical processing in mental arithmetic. This review extended its discussion of hierarchical “processing” to hierarchical “behavior”, that is, human action which has been referred to as being hierarchically composed. Several lesion and TMS studies supported the involvement of BA44 for hierarchical processing in the action domain. Lastly, the hierarchical organization of cognitive controls was discussed within the PFC, forming a cascade of top-down hierarchical processes operating along a posterior-to-anterior axis of the lateral PFC including BA44 within the network. It is proposed that PFC is actively involved in different forms of hierarchical processing and specifically BA44 may play an integral role in the process. Taking levels of proficiency and subcortical areas into consideration may provide further insight into the functional role of BA44 for hierarchical processing.

Recursion in action: An fMRI study on the generation of new hierarchical levels in motor sequences

“…This bilateral network included M1S1 and PMC, cerebellum, LOC, pallidum, putamen, and thalamus. Interestingly, in this study, which focused on the motor domain, we did not find evidence that these generative processes recruited IFG, an area thought to play an important role in the processing of hierarchies across domains (Fadiga et al, ; Fitch & Martins, ; Jeon, ). Although there was higher global activity within right BA 44 in Recursion compared with Iteration, this activity neither survived multi‐comparison p ‐value correction, nor was it specific for Recursion, being present also in the Repetition > Iteration contrast.…”

“…This bilateral network included M1S1 and PMC, cerebellum, LOC, pallidum, putamen, and thalamus. Interestingly, in this study, which focused on the motor domain, we did not find evidence that these generative processes recruited IFG, an area thought to play an important role in the processing of hierarchies across domains Jeon, 2014 not specific to the processing of hierarchical relations, but to some other processes, which we discuss below.…”

“…Based on current views that IFG is involved in the processing of hierarchies across many domains (e.g., language, music and action, as reviewed by Fadiga et al, 2009;Jeon, 2014) and in line with models of a posterior-to-anterior gradient of lateral PFC for hierarchical organization of actions (Badre, 2008;Koechlin & Summerfield, 2007), we hypothesized lateral PFC, and particularly IFG, to support motor generation of new hierarchical levels in our Recursive rule condition. However, we did not find evidence for involvement of this area in the generation of new hierarchical levels.…”

Shared neural and cognitive mechanisms in action and language: The multiscale information transfer framework

“…Hierarchically organized la2guage and motor sequences draw on common neural circuits. Within these circuits, which are generally attributed to the left perisylvian cortex, Broca's area (i.e., broadly premotor area BA 44 and BA 45) has been singled out as a prime candidate for containing a processor critically engaged in the production and comprehension of hierarchically structured sequences across different modalities, including language and motor sequences (Clerget, Andres, & Olivier, ; Clerget, Winderickx, Fadiga, & Olivier, ; Fadiga, Craighero, & D'Ausilio, ; Fitch & Martins, ; Jeon, ; Koechlin & Jubault, ; Pulvermüller & Fadiga, ; Tettamanti & Weniger, ). Thus, syntactic comprehension deficits induced by brain lesions in the left perisylvian cortex have been shown to correlate with impairments in the high‐level sequencing of certain complex actions and utterances (Fazio et al, ).…”

Interaction between Perceived Action and Music Sequences in the Left Prefrontal Area

“…There is a posterior-anterior functional gradient of the prefrontal area depending on the level of the temporal organization of action (Koechlin and Jubault, 2006; for reviews, see Koechlin and Summerfield, 2007 and Jeon, 2014): the activation of BA 6, BA 44, and BA 45 are involved in action planning of single acts, simple chunks, and superordinate chunks, respectively (Koechlin and Jubault, 2006). Thus, despite a difference between the planning and perception of action, if an enhancement of activation is found in BA 6 or BA 44, for instance, action perception is assumed to experience interference from the sound sequence at the level of processing individual finger movements, such as E-D-C-D-E-E-E (in the case of melody M), or at the level of processing simple chunks, such as [EDCD]-[EEE].…”