Encoding of Prospective Tasks in the Human Prefrontal Cortex under Varying Task Loads

Abstract

Successful realization of planned actions requires the brain to encode intentions over delays. Previous research has indicated that several regions in the rostral or anterior prefrontal cortex (PFC) encode delayed intentions. However, different processes may encode the same future task depending on task load during the delay. This difference may depend on the computational resources available when the delay is occupied with an ongoing task and when it is task-free. Here we directly investigated and compared the representation of delayed intentions in the human brain in the presence and absence of ongoing task load during the delay. We acquired fMRI data in combination with an event-based prospective memory design where human subjects remembered to perform the same future tasks over occupied and task-free delays. We used time-resolved multivoxel pattern classification and found that: (1) rostrolateral PFC (BA 46) encoded the delayed intention during both delay types; (2) rostromedial PFC (BA 10) encoded the intentions during occupied delays; whereas (3) a variety of more posterior regions, including the anterior cingulate cortex (BA 24), the supplementary motor area (BA 6), and the precuneus, encoded intentions during task-free delays. Overall, the medial PFC encoded delayed intentions more rostrally in the presence of an ongoing delay task and more caudally in its absence. Thus, rostromedial PFC may play a specialized role in the encoding of prospective memory that depends on higher computational demands (e.g., given higher task load during the delay). In contrast, the rostrolateral PFC is a more general area that encodes future intentions regardless of task load.

Language control in bilinguals: Intention to speak vs. execution of speech

“…speaking a language different from the one used previously. This interpretation is consistent with other studies that have linked the precuneus to a fronto-parietal control network responsible for directing selective attention (Dosenbach et al, 2007;Utevsky, Smith, & Huettel, 2014), and to studies showing the involvement of the precuneus in selecting and maintaining the intention of performing specific future tasks (prospective intentions, Burgess, Gonen-Yaacovi, & Volle, 2011;Momennejad & Haynes, 2013;Schacter, Addis, & Buckner, 2007;Soon, He, Bode, & Haynes, 2013). During the language execution phase we find distinct neural activity depending on which language is spoken.…”

Medial Prefrontal Cortex Predicts Internally Driven Strategy Shifts

“…Thus, the observed exploration of alternative strategies does not seem to be driven by unreliability, conflict or errors, as in previous studies (Botvinick et al, 2001; Collins and Koechlin, 2012; Daw et al, 2006; Donoso et al, 2014; Nassar et al, 2010). Rather, our findings would better relate with previous evidence showing the involvement of MPFC in deciding which task to perform in the future (Haynes et al, 2007; Momennejad and Haynes, 2013; Soon et al, 2013; Wisniewski et al, 2014). Note, however, that in the above-mentioned studies a (mostly a priori specified) rule was decoded from brain activity, whereas our study decoded stimulus features.…”

Neural evidence of the strategic choice between working memory and episodic memory in prospective remembering

“…Only voxels that showed enhanced signal in PM+OG trials were included. The reverse contrast (OG-only > PM+OG trials) revealed a network of voxels, including in the anterior medial prefrontal cortex, that deactivated with the addition of the PM task (Gilbert, 2011; Momennejad & Haynes, 2012, 2013). However, pattern classification of PM stimulus processing (target and distractor pictures) from these regions was at chance levels and therefore these voxels were excluded from further analysis.…”