Impaired awareness of motor intention in functional neurological disorder: implications for voluntary and functional movement.

BACKGROUND: Functional neurological disorders (FNDs), also known as conversion disorder, are unexplained neurological symptoms unrelated to a neurological cause. The disorder is common, yet poorly understood. The symptoms are experienced as involuntary but have similarities to voluntary processes. Here we studied intention awareness in FND. METHOD: A total of 26 FND patients and 25 healthy volunteers participated in this functional magnetic resonance study using Libet's clock. RESULTS: FND is characterized by delayed awareness of the intention to move relative to the movement itself. The reporting of intention was more precise, suggesting that these findings are reliable and unrelated to non-specific attentional deficits. That these findings were more prominent with aberrant positive functional movement symptoms rather than negative symptoms may be relevant to impairments in timing for an inhibitory veto process. Attention towards intention relative to movement was associated with lower right inferior parietal cortex activity in FND, a region early in the processing of intention. During rest, aberrant functional connectivity was observed with the right inferior parietal cortex and other motor intention regions. CONCLUSIONS: The results converge with observations of low inferior parietal activity comparing involuntary with voluntary movement in FND, emphasizing core deficiencies in intention. Heightened precision of this impaired intention is consistent with Bayesian theories of impaired top-down priors that might influence the sense of involuntariness. A primary impairment in voluntary motor intention at an early processing stage might explain clinical observations of slowed effortful voluntary movement, heightened self-directed attention and underlie functional movements. These findings further suggest novel therapeutic targets.

Selective prefrontal serotonin depletion impairs acquisition of a detour-reaching task.

We have recently shown that serotonin in the primate orbitofrontal cortex (OFC) contributes to the flexible control of behaviour. 5,7-dihydroxytryptamine-induced 5-HT depletions of OFC impair performance on a serial reversal discrimination task [Clarke et al. (2004)Science, 304, 878-880]. The deficit is characterized by perseverative responding to the previously rewarded stimulus, a deficit similar to that seen following lesions of the intrinsic neurones of the OFC [Dias et al. (1996)Nature, 380, 69-72]. The effect is neurochemically selective as dopaminergic lesions of the OFC, induced by 6-hydroxydopamine, have no effect [Clarke et al. (2006)Cerebral Cortex]. In order to test for the generality of the effect of serotonin on orbitofrontal processing and, in particular, its effects on flexible behaviour, the present study investigated the effects of serotonin depletions of OFC on performance of another task dependent upon an intact OFC, the detour-reaching task [Wallis et al. (2001)European Journal of Neuroscience, 13, 1797-1808]. Successful performance of this task requires inhibition of the animal's prepotent response tendency to reach directly along its line of sight to the reward. Compared with sham-operated controls, we found that lesioned monkeys made significantly more barrier reaches directly along their line of sight to the visible reward during task acquisition. This finding provides further support for the role of prefrontal serotonin in inhibitory control processes specifically in tasks sensitive to OFC dysfunction.