Distinct modulation of event-related potentials during motor preparation in patients with motor conversion disorder.

OBJECTIVE: Conversion paresis patients and healthy people feigning weakness both exhibit weak voluntary movement without detectable neuropathology. Uniquely, conversion patients lack a sense of conscious awareness of the origin of their impairment. We investigated whether conversion paresis patients show distinct electroencephalographic (EEG) markers associated with their unconscious movement deficits. METHODS: Six unilateral upper limb conversion paresis patients, 12 feigning participants asked to mimic weakness and 12 control participants performed a precued reaction time task, requiring movements of either hand, depending on precue information. Performance measures (force, reaction and movement time), and event-related EEG potentials (ERP) were compared, between groups and across hands or hemisphere, using linear mixed models. RESULTS: Feigners generated the same inter-hand difference in reaction and movement time as expressed by patients, even though no specific targets were set nor feedback given on these measures. We found novel ERP signatures specific to patients. When the symptomatic hand was precued, the P3 ERP component accompanying the precue was dramatically larger in patients than in feigning participants. Additionally, in patients the earlier N1 ERP component was diminished when the precue signalled either the symptomatic or asymptomatic hand. CONCLUSIONS: These results are consistent with previous suggestions that lack of awareness of the origin of their symptoms in conversion disorder patients may result from suppression of brain activity normally related to self-agency. In patients the diminished N1 to all precues is consistent with a generalised reduction in cognitive processing of movement-related precues. The P3 enhancement in patients is unlikely to simply reflect changes required for generation of impaired movements, because it was not seen in feigners showing the same behavioural deficits. Rather, this P3 enhancement in patients may represent a neural biomarker of unconscious processes, including additional emotional loading, related to active suppression of brain circuits involved in the attribution of self-agency

The diagnostic accuracy of selected neurological tests

The diagnostic value and reliability of selected neurological clinical tests was studied in control subjects with normal neuroimaging (n = 42), and subjects with a focal brain lesion (n = 38). The items were studied by two examiners blinded to group membership and using standardized protocols, and subsequentlyby a neurologist who was not blinded to diagnosis. The positive likelihood ratios ranged from1.06 (pronator drift) to 22.11 (single leg stance with eyes open, while the negative likelihood ratios ranged from 0.47 (tandem gait) to 0.97 (pupil symmetry). Three items (single leg stance – eyesclosed – firm surface; single leg stance – eyes open – foam surface; and tandem gait) successfully distinguished between the two groups (odds ratio p < 0.05). The inter-rater reliability was generally poor, with only tandem gait showing excellent agreement (kappa [K] = 0.92). Tandem gait was the only item to show noteworthy agreement (K = 0.93) between the examiners and the neurologist. The tests varied considerably in their ability to detect radiologically demonstrated structural brain lesions, and several items were poorly reproducible, questioning their value as part of a routine neurological examination

Normative values for three clinical measures of motor performance used in the neurological assessment of sports concussion

Postural control and motor coordination are essential components of normal athletic activity. Tasks involving balance and coordination areused to determine neurological function in sports-related concussion. Determining normative values for these tasks is therefore essential toprovide sports medicine professionals with a frame of reference with which to interpret clinical measures obtained from players suspected ofsustaining a concussion

Grand mean EEG waveforms.

<p>(A) Symptomatic (left) hand, recording from contralateral occipital cortex. Top plot shows average across entire trial duration, dashed lines at t = −2.0 s and t = 0 s indicate precue and imperative stimulus onsets, grey horizontal bar shows precue duration. Inset panels zoom on precue onset (left; visual ERP) and before stimulus onset (right; terminal CNV). (B) Asymptomatic (right) hand, recording from contralateral occipital cortex. (C) As for A, recording from motor cortex contralateral to the symptomatic hand. (D) As for B, recording from motor cortex contralateral to the asymptomatic hand. Negative upwards in all plots.</p

Quantification of ERP measures.

<p>(A–B) Mean (+ SEM) occipital N1 amplitude for symptomatic and asymptomatic hand precues respectively. Black bars, left hemisphere; grey bars right hemisphere. (C–D) P3 amplitudes at central electrodes. (E–F) P3 amplitudes at occipital electrodes. (G–H) CNV amplitudes at central electrodes. Negative upwards in all graphs. *<i>P</i>&lt;.05, **<i>P</i>&lt;.01.</p

Characteristics of participants.

a<p>Sensory deficits in the symptomatic limb:+small sensory deficits (some numbness on the symptomatic side);++moderate sensory deficits (some numbness on symptomatic side plus decreased sensation for light touch, vibration and temperature);+++severe sensory deficits (some numbness, tingling on symptomatic side, decreased sensation for light touch, vibration and temperature plus presence of vertigo, dizziness).</p>b<p>MVC force values for the feigners and controls for ‘symptomatic’ and ‘asymptomatic’ hand columns correspond to the left and right hands, respectively.</p>c<p>Diagnoses present within 12 months prior to testing, as assessed by the Composite International Diagnostic Interview (CIDI-Auto v2.1) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062539#pone.0062539-World1" target="_blank">[43]</a>. DSM-IV categories: 300.23 social phobia; 296.23 major depressive disorder, single episode, severe without psychotic features; 300.02 generalised anxiety disorder; 300.29N specific phobia, natural environment type.</p><p>Clinical details of each patient including individual force data for the maximum voluntary contraction (MVC) task, and group details of the feigners and controls including mean (± SD) force data for the MVC task.</p