Planning Goal-Directed Actions: fMRI Correlates in Humans and Monkeys

Citation

Iyer, Asha Muthuraman (2008) Planning Goal-Directed Actions: fMRI Correlates in Humans and Monkeys. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Q6P2-GC02. https://resolver.caltech.edu/CaltechETD:etd-06102008-162347

Abstract

In performing goal-directed actions, primates (humans and monkeys) flexibly select and plan appropriate behavioral responses. However, while a network of frontoparietal regions are traditionally implicated in the transformation of sensory input from the environment into these spatial, goal-directed movements, the type of information encoded in their activity remains nebulous.

This work first addresses the long-standing query as to whether this activity represents a prospective planning of the upcoming action, or a retrospective sensory representation of goals. In an fMRI experiment, subjects performed delayed-reach tasks, in which mnemonic and attentional demands were held constant. BOLD signals showed that the posterior parietal cortex (PPC) and premotor regions exhibit activity specifically related to the planning of upcoming actions.

Additionally, to select and plan the optimal action, the expected consequences of potential responses need to be assessed. To determine whether and how potential outcomes mold action planning activity, subjects were scanned while they performed a demanding motor task to obtain monetary gains or losses contingent on their performance. Monetary consequences modulated activity throughout the action-planning network, most significantly in PPC, as well as in reward structures. While reward areas reflected the expected value of a trial, frontoparietal activity was greatest for both high expected rewards and losses. Moreover, in frontoparietal areas, subjects’ beliefs about the likelihood of possible outcomes influenced BOLD signals, suggesting that cognitive biases may influence the planning of actions.

Finally, to compare human imaging findings to large body of related monkey electrophysiological experiments, humans and monkeys were scanned while performing the same delayed-saccade tasks. Frontoparietal oculomotor-planning areas in monkeys and putative homologs in humans evinced coherent response patterns, though prominent differences in the degree of contralaterality and the hemodynamic responses between the two species emerged.

In sum, these findings help characterize fundamental aspects of goal-directed action planning in both species.

Thesis Files