Functional Anatomy of Nonvisual Feedback Loops during Reaching: A Positron Emission Tomography Study

Abstract

Reaching movements performed without vision of the moving limb are continuously monitored, during their execution, by feedback loops (designated nonvisual). In this study, we investigated the functional anatomy of these nonvisual loops using positron emission tomography (PET). Seven subjects had to "look at" (eye) or "look and point to" (eye-arm) visual targets whose location either remained stationary or changed undetectably during the ocular saccade (when vision is suppressed). Slightly changing the target location during gaze shift causes an increase in the amount of correction to be generated. Functional anatomy of nonvisual feedback loops was identified by comparing the reaching condition involving large corrections (jump) with the reaching condition involving small corrections (stationary), after subtracting the activations associated with saccadic movements and hand movement planning [(eye-armjumping minus eye-jumping) minus (eye-arm-stationary minus eye-stationary)]. Behavioral data confirmed that the subjects were both accurate at reaching to the stationary targets and able to update their movement smoothly and early in response to the target jump. PET difference images showed that these corrections were mediated by a restricted network involving the left posterior parietal cortex, the right anterior intermediate cerebellum, and the left primary motor cortex. These results are consistent with our knowledge of the functional properties of these areas and more generally with models emphasizing parietal-cerebellar circuits for processing a dynamic motor error signal.

Time Course of Error Detection and Correction in Humans: Neurophysiological Evidence

“…Whereas on-line corrections in the double-step paradigm are performed even if the target displacement is not consciously detected (Prablanc and Martin, 1992), the error-correction mechanism studied in the present investigation is related to conscious detection and the intentional release of a corrective motor command using the contralateral limb. The anterior cingulate cortex is clearly involved in the type of paradigm used in the present investigation (Carter et al, 1998) but not in the on-line corrections in the double-step paradigm (Desmurget et al, 2001).…”

“…This is clearly different from paradigms in the motor domain, such as so-called double-step experiments involving subliminal target displacements (Prablanc and Martin, 1992). In a recent brain imaging study using this paradigm, a neural network including the cerebellum, posterior parietal cortex (PPC), and primary motor cortex was demonstrated to be involved in error correction (Desmurget et al, 2001). PPC has also been demonstrated to be important the correction of hand trajectories (Desmurget et al, 1999;Pisella et al, 2000).…”

Basal ganglia network mediates the control of movement amplitude

“…Imaging methods have been described in previous publications (Desmurget et al, 1998a, b;Turner et al, 1998;Desmurget et al, 2001). In brief, regional cerebral blood¯ow (rCBF) images were acquired with a Siemens ECAT Exact scanner, using a modi®ed autoradiographic method in 3-D mode.…”

“…The effects (and source of variance) in the statistical model were subject, task and repetition. Given the subjects' consistent task performance and the randomization procedure, repetition could be treated as replication, resulting in a two-way ANOVA (Turner et al, 1998;Desmurget et al, 2001). Because the present experiment is bounded by an explicit question, namely whether or not BG is selectively involved in the planning of movement amplitude, a planned approach was used for statistical analysis and the search volume was restricted to the BG complex.…”

Robotics and neuroscience: A rhythmic interaction

“…While rhythmic movements can be programmed by low level Central Pattern Generators (CPGs) (see e.g. Cohen, Rossignol, and Grillner (1988), Duysens and Van de Crommert (1998) and Swinnen (2002)), discrete movements also recruit higher cortical areas, that have been shown to play a role in the processing of sensory feedback (Desmurget et al, 2001). The level of feedback processing thus appears to be different in both kinds of movements.…”