Raw EMG traces of a representative trial during ankle dorsiflexion.

<p>Gray lines are trials without a SAS, black lines are trials with a SAS. Determined latencies are presented by a dot.</p

Mean acceleration (SE) of onset latencies of automatic postural responses in tibialis anterior (TA) during SAS-trials with and without a startle reflex in the sternocleidomastoid (SCM) muscle.

<p>The number of participants who showed trials with and without SCM reflexes is indicated on top of each bar. In all groups, acceleration of responses did not differ significantly between SAS-trials with and without a startle reflex in the SCM-muscle.</p

Mean step lengths and leg angles (SE) during backward perturbations.

<p>Patients with postural instability had significantly smaller step lengths than patients without postural instability, but step length did not differ between freezers and non-freezers. Step lengths were significantly shorter in patients without postural instability compared to controls. Leg angles were significantly smaller in patients with postural instability compared to patients without postural instability. Leg angles did not differ between freezers and non-freezers. Patients without postural instability had more negative leg angles compared to controls.</p

Participant characteristics.

<p><i>Data are mean (range)</i>. <i>UPDRS = MDS-Unified Parkinson’s disease rating scale part III (score/132)</i>, <i>N-FOGQ = New Freezing of Gait Questionnaire(score/33)</i>, <i>FAB = Frontal Assessment Battery (score/18)</i>.</p><p>Participant characteristics.</p

Ankle dorsiflexion.

<p><i>Values are mean (SD)</i>. <i>HY = Hoehn and Yahr stage</i>.</p><p>Ankle dorsiflexion.</p

Step onset and number of balance correcting steps.

<p><i>Values are mean (SD)</i>.</p><p>Step onset and number of balance correcting steps.</p

Average EMG-activity recorded in the tibialis anterior muscle of a single PD-patient (with freezing of gait and postural instability) during backward balance perturbations.

<p>Grey line represents perturbations with SAS (determined onset latency = 140 ms). Black line represents perturbations without SAS (determined onset latency = 145 ms).</p

Mean amplitudes (SE) of the automatic postural response in tibialis anterior (TA).

<p>HY = Hoehn and Yahr stage. Tibialis anterior amplitudes were significantly smaller in patients with postural instability compared to patients without postural instability, whereas they did not significantly differ between freezers and non-freezers. Amplitudes of tibialis anterior did not differ between patients without postural instability and controls.</p

Mean onset latencies (SE) of the automatic postural response in tibialis anterior (TA).

<p>HY = Hoehn and Yahr stage. A SAS significantly accelerated automatic postural responses. Latencies and their acceleration by the SAS did not differ between patients with and without postural instability. The SAS-induced acceleration of tibialis anterior responses was significantly attenuated in the freezers compared to the non-freezers. Non-freezers did not differ from controls.</p

Mean onset latencies of prime movers of postural responses (SE) to backward (tibialis anterior muscle) and forward (gastrocnemius medialis muscle) perturbations.

<p>*significant difference between trials with and without a SAS (main effect). +significant difference between anodal-tDCS and sham-tDCS (main effect).</p