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. 2016 Mar 23;6:23327. doi: 10.1038/srep23327

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Copyright © 2016, Macmillan Publishers Limited

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Indices of simulated behaviour: (a) maintenance, (b) perseverance and (c) switches of 12 randomly selected seeds, tested under four different conditions (on and off simulated treatment times high and low valued inputs). Histograms represent mean measures and standard deviation, per trial, under simulated on- and off- subthalamic stimulation, across reward conditions. Markers represent mean values per participant. Within each histogram, the markers have been grouped so that the squares represent measures recorded under the condition of low values and circles represent measures recorded under the condition of high values. Boxplots represent the distribution of within seed differences, with red markers used to highlight the presence of any outlier. Each measure reports the distribution of difference across value condition (left), and under either high (centre) or low (right) value separately. Both for the index of maintenance (a) and for the index of perseverance (b), the distribution of within seed differences shows these measures vary as a function of the treatment condition but they are not significantly affected by the value condition (F = 23.281, p = 0.001, and F = 39.881, p < 0.001, respectively). Conversely, in the measure of switches (c) we observed an interaction effect of the two variables of value and simulated treatment (F = 17.696, p = 0.001). When comparing on and off simulated DBS the number of switches decreases (standard motor suppression) under low values and it increases (excessive switching) under high value condition ((t(11) = 5.61, p < 0.001 and t(11) = −3.12, p = 0.009, respectively). If considered across value condition, the behaviour does not vary significantly as a function of the simulated treatment alone, which might explain the absence of effect found in the same measure for the first experiment, where no reward manipulation was included. Statistical significance (two-way repeated-measures ANOVA) expressed as follows: ***for p ≤ 0.001. Note we do not establish a quantitative comparison between the simulated selections and the reported behaviour of the patients as we prefer to highlight the direction of measure comparison. This choice is reflected in the simulation by the presence of slightly different timing and number of time intervals for the input changes.