Brain preparation before a voluntary action: Evidence against unconscious movement initiation
ABSTRACT Benjamin Libet has argued that electrophysiological signs of cortical movement preparation are present before people report having made a conscious decision to move, and that these signs constitute evidence that voluntary movements are initiated unconsciously. This controversial conclusion depends critically on the assumption that the electrophysiological signs recorded by Libet, Gleason, Wright, and Pearl (1983) are associated only with preparation for movement. We tested that assumption by comparing the electrophysiological signs before a decision to move with signs present before a decision not to move. There was no evidence of stronger electrophysiological signs before a decision to move than before a decision not to move, so these signs clearly are not specific to movement preparation. We conclude that Libet’s results do not provide evidence that voluntary movements are initiated unconsciously.
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ABSTRACT: This study examined cortical motor structures that are involved in preprogramming and execution of movements. In two independent experiments a response precuing task was employed that combined the recording of movement-related brain potentials (MRPs) with spatio-temporal source localization. Behavioral and MRP results indicated the utilization of advance information about movement direction and hand. Dipole source modeling of foreperiod MRPs revealed a reliable three-dipole solution with sources located in lateral and medial brain regions anterior to the precentral gyrus. These dipoles were located in the lateral premotor area (PMA) and supplementary/cingulate motor areas (SMA/CMA). Activity of the medial dipole increased with the extent of advance motor preparation, whereas lateral dipole activity revealed parallel preparation of both response hands when only partial information about movement direction was available. The dissociation in the strength and the onset of medial and lateral dipole activity indicated two phases of motor preparation. We propose that medial motor areas like SMA and CMA are involved in the assembling and selection of abstract movement programs, whereas lateral PMA and primary motor cortex are involved in effector-specific motor preparation.Cognitive Brain Research 11/2001; 12(2):207-24. · 3.77 Impact Factor
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ABSTRACT: Effects of movement advance information were assessed on the prestimulus amplitude of the lateralized readiness potential (LRP), on the contingent negative variation (CNV), and on reaction time (RT). In a precuing paradigm with movement parameters hand, direction, and force, partial precues provided advance information about either hand alone, hand plus force, or hand plus direction, and the full precue specified all response parameters. The full precue produced the shortest RTs and the largest CNV amplitude, precuing hand and force or hand and movement direction produced somewhat slower RTs and a somewhat smaller CNV amplitude, and precuing only hand yielded slowest RTs and the smallest CNV amplitude. In contrast, the LRP amplitude was largest for the full precue and was the same for the remaining precues. The CNV appears to index the central assembling of a motor program, and the LRP represents the implementation of the program at more peripheral levels.Psychophysiology 10/1998; 35(6):721 - 728. · 3.29 Impact Factor
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ABSTRACT: There has been a long controversy as to whether subjectively 'free' decisions are determined by brain activity ahead of time. We found that the outcome of a decision can be encoded in brain activity of prefrontal and parietal cortex up to 10 s before it enters awareness. This delay presumably reflects the operation of a network of high-level control areas that begin to prepare an upcoming decision long before it enters awareness.Nature Neuroscience 06/2008; 11(5):543-5. · 15.25 Impact Factor