Failure of explicit movement control in patients with functional motor symptoms

Abstract

Functional neurological symptoms are one of the most common conditions observed in neurological practice, but understanding of their underlying neurobiology is poor. Historic psychological models, based on the concept of conversion of emotional trauma into physical symptoms, have not been implemented neurobiologically, and are not generally supported by epidemiological studies. In contrast, there are robust clinical procedures that positively distinguish between organic and functional motor signs that rely primarily on distracting attention away from movement or accessing it covertly. We aimed to investigate the neurobiological principles underpinning these techniques and implications for understanding functional symptoms. We assessed 11 patients with functional motor symptoms and 11 healthy controls in three experimental set-ups, where voluntary movements were made either with full explicit control or could additionally be influenced automatically by factors of which participants were much less aware (one-back reaching, visuomotor transformation, and precued reaction time with variable predictive value of the precue). Patients specifically failed in those tasks where preplanning of movement could occur and under conditions of increasing certainty regarding the movement to be performed. However, they implicitly learned to adapt to a visuomotor transformation as well as healthy controls. We propose that when the movement to be performed can be preplanned or is highly predicted, patients with functional motor symptoms shift to an explicit attentive mode of processing that impairs kinematics of movement control, but movement becomes normal when such processes cannot be employed (e.g., during unexpected movement or implicit motor adaptation).

Force modulation deficits in complex regional pain syndrome: A potential role for impaired sense of force production

“…A contribution of attention deficits towards the affected limb seems plausible in this regard, given that CRPSAP patients showed more neglect-like symptoms with respect to their affected limb than CRPSnoAP patients. Interestingly, a significant role of attentional modulation has also been postulated in functional movement disorders (Edwards et al, 2011;Pareés et al, 2013), since patients with functional tremor performed better on a motor task that involved less explicit (i.e., more automatic) voluntary control (Pareés et al, 2013). This warrants further research aimed at identification of potentially shared pathophysiological aspects between CRPSAP and functional movement disorders.…”

Antisaccades and vergence abnormalities in functional movement disorders: A video-oculographic study

“…The results were analogous to the typical clinical findings in FMD, with disturbed volitional movements (antisaccades and vergence), and reflexive prosaccades were normal. The subclinical abnormalities in vergence could reflect the failure of explicit motor control, which has been demonstrated in FMD patients, rather than a specific dysfunction of the underlying neural circuit . Recent models involve attentional focus, working memory, and planning along with automatic response inhibition to carry out a correct antisaccade .…”

Functional neurological disorders: mechanisms and treatment

“…Exploring further the role of attention and self-agency, Parees et al conducted a series of experiments testing voluntary movements under full conscious control and various degrees of automatic control [49]. They showed that patients with functional neurological disorders performed particularly poorly in tasks that were highly predictable, as these situations allow a switch to an ''attentive self-focused action-monitoring mode''.…”