Research 1

Functional organization of the prefrontal cortex in humans

      The prefrontal cortex is divided into anatomically distinct sub-regions but their specific computational functions remain unclear. We combine fMRI and models of decision making developed in behavioral economics and mathematical psychology to investigate the computations performed by distinct prefrontal cortex regions. We use paradigms investigating different processes involved during cognitive control (eg. task switching), perceptual and value-based decision making.

      For example, we have shown that manipulating the probability and the history of sequences of decisions have profound influence on the way the prefrontal cortex is recruited. Specifically, the dorsolateral prefrontal cortex and the anterior medial prefrontal cortex serve distinct roles during task switching: the dorsolateral prefrontal cortex is engaged when sequences of decisions are performed in unpredictable order while the anterior medial prefrontal cortex is recruited when decisions are done in a predictable order, likely reflecting that this brain region monitors which task is supposed to occur next. These results indicate a hierarchic organization of the prefrontal cortex along a posterio-anterior axis and a medio-lateral axis as the task becomes more endogenously guided. This medio-lateral division of the prefrontal cortex in the domain of task sequences generalizes to the cognitive domain the medio-lateral premotor cortex division previously proposed in the motor domain for self-initiated versus externally guided motor sequences.

      More recently, we found that the extent of damage to the fronto-polar cortex, which is disproportionally larger in humans relative to the rest of the brain than it is in the ape’s brain, predicts impairment in the management of multiple goals. The integrity of the fronto-polar cortex is thus necessary to perform tasks that require subjects to maintain a primary goal in mind while processing secondary goals, a crucial component of complex human cognitive abilities.

      We also demonstrated that the anterior lateral orbitofrontal cortex, a phylogenetically recent structure, processes monetary gains, while the posterior lateral orbitofrontal cortex, phylogenetically older, processes more basic erotic stimuli. This dissociation between orbitofrontal cortex representations of primary and secondary rewards parallels views on lateral prefrontal cortex organization in cognitive control, suggesting an increasing trend in complexity along a postero-anterior axis according to more abstract representations.

      We are currently investigating whether complex choices, such as moral and social decisions involve common prefrontal mechanisms that are involved in perceptual decision making.

Selected papers:

- P. Domenech and J-C Dreher. Decision threshold modulation in the human brain, J Neurosci, 30(43):14305-14317, 2010
- G. Sescousse, J. Redoute, J-C Dreher. The architecture of reward value coding in the orbitofrontal cortex, J Neurosci, 30(39):13095-104, 2010
- J-C Dreher, E. Koechlin, M. Tierney, J. Grafman. Damage to the Fronto-Polar Cortex Is Associated with Impaired Multitasking. PLoS ONE. 3(9):e3227, 2008.
- J-C Dreher, J. Grafman. Dissociating the roles of the rostral anterior cingulate and the lateral prefrontal cortices in performing two tasks simultaneously or successively, Cerebal Cortex, 13(4), 329-39, 2003.
- J-C. Dreher, K Berman. Fractionating the neural substrate of cognitive control processes, Proceedings of the National Academy of Sciences USA, 99 (22), 14595-14600, 2002.
- J-C. Dreher, E Koechlin, S.O Ali, J Grafman. The roles of timing and task order during task switching, Neuroimage, 17 (1), 95-109, 2002.