Figure 4.

This schematic illustrates the hierarchical anatomy we presume underlies false inference in patients with functional motor symptoms (both weakness and ‘positive’ phenomena such as tremor). In normal movement, we propose that predictions regarding the sensory consequences of intended movement arise at a high hierarchical level (here pre-supplementary motor area) and are propagated down the motor hierarchy, producing a proprioceptive prediction error (peripherally) that is fulfilled by movement. In functional motor symptoms we propose that an abnormal prior expectation related to the dynamics/scaling of movement is formed within an intermediate motor area (here the supplementary motor area). This prior is afforded abnormal precision by attentional processes (thick blue arrow) that cause intermediate level motor predictions (thick black arrow) to elicit movement and prediction errors (thick red arrow) to report the unpredicted content of that movement to higher cortical areas (here, pre-supplementary motor area). The secondary consequence of these prediction errors is that prefrontal regions will try to explain them away in terms of a symptomatic interpretation or misattribution of agency to external causes; in short, a failure to realize the movement was intended. Forward connections convey prediction error (red), backward connections convey predictions (black) and descending attentional modulatory connections (blue). pSMA = pre-supplementary motor area; M1 = primary motor cortex; SMA = supplementary motor area.