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FIGURE 20.4 DBS in the STn of dopamine-depleted PD patients eliminates the retrieval, but not the encoding distortion. Estimate distributions in real time and time relative to the median time (left panels) and motor scores (right panels), for both training and testing days, in three groups of PD patients treated with DBS in the STn. The two groups trained ON DBS (ON-ON and ON-OFF) are shown in open circles (top and middle rows, respectively). Both groups show a slight, but reliable overestimation for both targets during training, while asymmetrical performance is seen during testing. Migration of estimates occurs in the testing session only OFF (ON-OFF group, middle panel, black points) but not ON DBS, indicating a beneficial effect of stimulation on retrieval. This is to be contrasted with the overestimation seen during testing stimulator ON (ON-ON group, upper panel, white points; OFF-ON group, lower panel, gray points). Training while stimulator OFF produces migration (OFF-ON group, lower panel, black points) that apparently masks the rightward shift, subsequently revealed in the testing session stimulator ON. The presence of a corrective mechanism, somehow effective under stimulation and in the presence of feedback, is implied by the different order of magnitude of the rightward shift as a function of whether training occurred with stimulator ON (ON-ON group, upper panel, gray) or OFF (OFF-ON group, lower panel, gray).

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