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Altered awareness of voluntary action after damage to the parietal cortex

Abstract

A central question in the study of human behavior is the origin of willed action. EEG recordings of surface brain activity from human subjects performing a self-initiated movement show that the subjective experience of wanting to move follows, rather than precedes, the 'readiness potential'—an electrophysiological mark of motor preparation. This raises the issue of how conscious experience of willed action is generated. Here we show that patients with parietal lesions can report when they started moving, but not when they first became aware of their intention to move. This stands in contrast with the performance of cerebellar patients who behaved as normal subjects. We thus propose that when a movement is planned, activity in the parietal cortex, as part of a cortico-cortical sensorimotor processing loop, generates a predictive internal model of the upcoming movement. This model might form the neural correlate of motor awareness.

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Figure 1: Task procedure and EEG recording sites.
Figure 2: Behavioral data.
Figure 3: Samples of EEG recording.
Figure 4: Lesioned cortical region (blue area) common to all five parietal patients.

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Acknowledgements

The authors wish to thank J.R. Duhamel for helpful discussion on a first draft, L. Granjon and B. Messaoudi for assistance during EEG and EMG recording, and A. Cheylus and M. Thevenet for help analyzing EEG data and doing lesion reconstruction. This research was supported by Centre National de la Recherche Scientifique (CNRS).

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Correspondence to Angela Sirigu.

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Supplementary information

Supplementary Fig. 1

Event-related potentials (ERPs) recorded during the control condition (beep). Black line: ERP grand average for normal controls (N = 5); Colored lines: ERPs for each parietal patient. (N= 4). Signal was averaged over beep-locked epochs (from -200 ms to +1000 ms with respect to beep occurrence). Average reference was applied. The first 200 ms of each epoch were used for baseline correction. As shown in the plot, the main components of this stimulus-related activity, namely P100, N200 and P300 are similar in both normal controls and parietal patients. It is important to note that P300 is a late component related to the cognitive processing of the stimulus. A statistical comparison between the two groups for P300 amplitude showed no differences (mean controls 4.421 SD 2.452, mean parietal 3.396 SD 3.099, Mann-Whitney U Test for P300: U= 6.0 Z= 0.9798 P = 0.3272). (JPG 30 kb)

Supplementary Fig. 2

Methods for computing the onset of the RP. We defined the onset of the RP as follows. First, we manually selected an interval of interest that we estimated contained the RP (delimited by the two vertical orange lines). We then computed a linear regression of the data within this interval (orange curves). Parallel lines bounding the minimum and maximum deviation of the RP from the regression line were traced above and below it. A new interval was then defined by extending these lines to include all of the RP variation contained within these bounds. The RP onset was set at the point within this interval at which the value of the RP is at its lowest (i.e, the most positive potential). (JPG 24 kb)

Supplementary Fig. 3

Distribution of the responses given by each subject for the three groups across the three experimental conditions (M-time, W--time, S-time). X-axis: time scale, referred to the clock's face; Y-axis: number of responses given by the subject. (a) controls subjects (CTR 1-5), (b) cerebellar patients (CER 1-5), (c) parietal patietns (PAR 1-5). (PDF 66 kb)

Supplementary Fig. 4

RP controlateral to the responding hand for each parietal patient for M and W condition. (JPG 31 kb)

Supplementary Table 1 (PDF 12 kb)

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Sirigu, A., Daprati, E., Ciancia, S. et al. Altered awareness of voluntary action after damage to the parietal cortex. Nat Neurosci 7, 80–84 (2004). https://doi.org/10.1038/nn1160

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