Aberrant supplementary motor complex and limbic activity during motor preparation in motor conversion disorder

Abstract

Background Conversion disorder is characterized by unexplained neurological symptoms presumed related to psychological issues. The main hypotheses to explain conversion paralysis, characterized by a lack of movement, include impairments in either motor intention or disruption of motor execution, and further, that hyperactive self-monitoring, limbic processing or top-down regulation from higher order frontal regions may interfere with motor execution. We have recently shown that conversion disorder with positive abnormal or excessive motor symptoms was associated with greater amygdala activity to arousing stimuli along with greater functional connectivity between the amgydala and supplementary motor area. Here we studied patients with such symptoms focusing on motor initiation. Methods Subjects performed either an internally or externally generated two-button action selection task in a functional MRI study. Results Eleven conversion disorder patients without major depression and 11 age- and gender-matched normal volunteers were assessed. During both internally and externally generated movement, conversion disorder patients relative to normal volunteers had lower left supplementary motor area (SMA) (implicated in motor initiation) and higher right amygdala, left anterior insula and bilateral posterior cingulate activity (implicated in assigning emotional salience). These findings were confirmed in a subgroup analysis of patients with tremor symptoms. During internally versus externally generated action in CD patients, the left SMA had lower functional connectivity with bilateral dorsolateral prefrontal cortices. Conclusion We propose a theory in which previously mapped conversion motor representations may in an arousing context hijack the voluntary action selection system which is both hypoactive and functionally disconnected from prefrontal top-down regulation.

Brain circuits implicated in psychogenic paralysis in conversion disorders and hypnosis

“…Similar evidence has been gathered in recent studies [101][102][103] concerning patients with psychogenic movement disorders such as tremor or dystonia (i.e., positive rather negative motor symptoms), although pointing to the role of different circuits connecting the amygdala to SMA (see also review by Voon et al in this issue). Future research should use more advanced connectivity measures such as dynamic causal modelling (DCM) and compare different conversion patient groups during different symptomatic conditions (pre-vs. post-recovery) to gain better insights into such interactions between motor control and emotion/motivation systems.…”

“…On the other hand, however, unlike the classic view, conversion and hypnosis appear to act on behavior and perception via partly distinct brain circuits. In conversion, modulations of motor and sensory awareness might primarily be driven by an increased recruitment of regions in VMPFC, implicated in the access to self-relevant affective representations and memories [17,104,105,107], as well as other subcortical limbic regions such as the amygdala [45,79,101,102]. These areas might influence movement, sensation, and self-awareness more broadly by promoting or suppressing certain patterns of behaviors through modulatory inputs to motor or sensory pathways (as observed for more primitive adaptive reactions to threat, see [47,104,110]), and/or by imbuing behavior with particular affective and self-relevant associations though an integration of sensorimotor activity with internal representations retrieved from memory or imagery.…”

Aversive stimuli exacerbate defensive motor behaviour in motor conversion disorder

“…Viewing unpleasant images might lead to an overestimation of threat and self-relevance, possibly through retrieved episodic memories linked to negative life events (Brown, 2004). Increased PCC activity was also observed in patients with functional tremor by Voon et al (2011), who concluded that patients may aberrantly assign "stimuli, states or memories as selfrelevant or salient". Similarly, Cojan et al (2009) found greater PCC activity during motor preparation in a patient with functional paralysis, thought to reflect abnormal self-referential processes that may alter subjective motor agency.…”

Excitatory and inhibitory conversive experiences: neurobiological features involving positive and negative conversion symptoms

“…Furthermore, a subgroup of patients suffering from conversion tremor presented less connectivity between the supplementary motor area and the bilateral dlPFC (Voon et al, 2011). A decreased activation in parietal areas has been found as well as poorer connectivity between parietal cortex, limbic areas and sensorimotor cortex (Hallett, 2010).…”

“…Voon proposed for this type of conversion symptoms a theory according to which conversion motor representations previously mapped could trigger, in an alertness context, the voluntary action selection system which would be hypoactive and functionally disconnected from regulatory prefrontal top-down mechanisms (Voon et al, 2011). In this sense, a failure on high-order prefrontal regulation of motor control has been postulated.…”