[Abstract Title]. - Society for Neuroscience

Topic: F.01.g. Decision making and reasoning
Title: Sensory-motor mechanisms in human parietal cortex underlie arbitrary visual decisions
Authors: A. TOSONI 1 , G. GALATI 2 , G. ROMANI 1 , *S. ASTAFIEV 3 , M. CORBETTA 4 ;
1 Dept. of Clin. Sci. and Bioimaging, G. D‟Annunzio University, Inst. for Advanced Biomed.
Technologies, G. D‟Annunzio Fndn., Chieti, Italy; 2 Inst. for Advanced Biomed. Technologies,
G. D‟Annunzio Foundation, Dept. of Psychology, Sapienza University, Neuroimaging
Laboratory, Santa Lucia Fndn., Roma, Italy; 3 Dept Radiol, Washington Univ. Sch. of Med., St
Louis, MO; 4 Dept. of Clin. Sci. and Bioimaging, Inst. for Advanced Biomed. Technologies, G.
D‟Annunzio Foundation, Departments of Neurology, Radiology, Anat. & Neurobiology,
Washington Univ. Sch. of Med., St.Louis, MO
Abstract: The neural mechanism underlying perceptual decision-making has been recently
conceptualized as an integrative process in which sensory evidence supporting different response
options accumulates gradually over time. In the critical neurophysiological experiments, oculomotor
neurons in the lateral intraparietal (LIP) area, responsive to visual motion, accumulate
over time motion information in favour of the specific oculomotor choice they are selective for
(Shadlen et al., 1996; 2001). It is unclear, however, whether this mechanism generalizes to more
complex humans decisions based on arbitrary stimulus-response associations. Here we tested
with fMRI 12 subjects while performing a decision task requiring to arbitrarily associate visual
stimuli (faces or places) to different actions (eye or hand pointing movements). On each trial the
amount of sensory evidence available was varied by adding noise to the images. By using a ROIbased
approach, we showed that activity of two hand pointing-selective regions in posterior
parietal cortex was modulated, at a moment in which decisions were being formed, by the level
of sensory evidence in favour of a manual response, the position of the action target, and even
the outcome of the decision in the absence of helpful sensory information. Critically, the
modulation by sensory evidence did not reflect greater sensory selectivity of parietal cortex to
place stimuli that were associated with pointing responses. Therefore, human posterior parietal
cortex contains a sensory-motor mechanisms, completely triggered by contextual stimulusresponse
associations, that accumulates sensory evidence toward the behavioural outcome of an
arbitrary decision. This mechanism is specific to posterior parietal cortex as pointing-selective
regions in frontal cortex were not modulated either by sensory evidence levels or outcome. We
conclude that visual decisions in human subjects do not necessarily involve high-level
representations, independent of motor systems (Heekeren et al., 2006). Rather, decision
processes seem to be embodied in the direct transformations between relevant sensory and motor
representations, with motor circuitries querying sensory systems for evidence toward learned
behavioural choices. More generally, these findings support the emerging idea of “embodied
cognition”(Wilson 2002) according to which abstract cognitive functions do not depend on
specialized modules, but are built on simpler sensory-motor mechanisms.
Disclosures: A. Tosoni, None; G. Galati, None; G. Romani, None; S. Astafiev , None; M.
Corbetta, None.