Delayed beta synchronization after movement of the more affected hand in essential tremor

(A)symmetry during gait initiation in people with Parkinson's disease: A motor and cortical activity exploratory study

Background

Gait asymmetry and deficits in gait initiation (GI) are among the most disabling symptoms in people with Parkinson's disease (PwPD). Understanding if PwPD with reduced asymmetry during GI have higher asymmetry in cortical activity may provide support for an adaptive mechanism to improve GI, particularly in the presence of an obstacle.

Objective

This study quantified the asymmetry of anticipatory postural adjustments (APAs), stepping parameters and cortical activity during GI, and tested if the presence of an obstacle regulates asymmetry in PwPD.

Methods

Sixteen PwPD and 16 control group (CG) performed 20-trials in two conditions: unobstructed and obstructed GI with right and left limbs. We measured, through symmetry index, (i) motor parameters: APAs and stepping, and (ii) cortical activity: the PSD of the frontal, sensorimotor and occipital areas during APA, STEP-I (moment of heel-off of the leading foot in the GI until the heel contact of the same foot); and STEP-II (moment of the heel-off of the trailing foot in the GI until the heel contact of the same foot) phases.

Results

Parkinson's disease showed higher asymmetry in cortical activity during APA, STEP-I and STEP-II phases and step velocity (STEP-II phase) during unobstructed GI than CG. However, unexpectedly, PwPD reduced the level of asymmetry of anterior-posterior displacement (p < 0.01) and medial-lateral velocity (p < 0.05) of the APAs. Also, when an obstacle was in place, PwPD showed higher APAs asymmetry (medial-lateral velocity: p < 0.002), with reduced and increased asymmetry of the cortical activity during APA and STEP-I phases, respectively.

Conclusion

Parkinson's disease were not motor asymmetric during GI, indicating that higher cortical activity asymmetry can be interpreted as an adaptive behavior to reduce motor asymmetry. In addition, the presence of obstacle did not regulate motor asymmetry during GI in PwPD.

Disturbed post-movement beta synchronization in Wilson's disease with neurological manifestation

We analyzed the changes of post-movement beta synchronization (PMBS) of the electroencephalogram (EEG) in Wilson's disease with neurological manifestation. Our aim was to determine if PMBS in Wilson's disease is altered in a different way than in Parkinson's disease or in essential tremor. Our purpose was to find out whether the analysis of PMBS could help the diagnosis in ambiguous cases. Ten patients with neurological manifestation of Wilson's disease and ten controls performed self-paced movements with the dominant hand during EEG acquisition. Five electrodes above the sensorimotor cortex were selected for evaluation (C3, C1, Cz, C2, C4) as contralateral (C); contralateral medial (CM); medial (M); ipsilateral medial (IM); ipsilateral (I) relative to the dominant hand. Power and latency of PMBS were calculated by time resolved power spectral analysis with multitaper method. PMBS power in the C electrode position was significantly lower in patients than in controls, its contralateral preponderance disappeared in the patient group. In every location, latency of PMBS was significantly longer in the Wilson group compared to controls. More altered PMBS could be measured in patients with both basal ganglia and cerebellar involvements. Since decreased power of PMBS was observed in Parkinson's disease and increased latency in essential tremor, the combined change of PMBS can indicate pathology of different neural circuits and may help the diagnosis in challenging cases.

Mirror movements in patients with essential tremor

Mirror movements (MM), which occur in age-related neurodegenerative diseases such as Parkinson's disease (PD), have never been studied in essential tremor (ET). The objective of this work is to study the prevalence and clinical correlates of MM in ET cases and controls. In a clinical-epidemiological study in New York, participants performed repetitive motor tasks; MM (hands and feet) were rated. MM occurred in 35/107 (32.7%) ET cases versus 23/97 (23.7%) controls (OR 1.56, P = 0.16). Total MM score was 2x higher in cases (3.9 +/- 7.7 vs. 1.9 +/- 3.9, P = 0.02). MM (hands) occurred in 16 (15.0%) cases versus 5 (5.2%) controls (OR 3.24, P = 0.03) and total hand MM score was three to four times higher in ET cases (1.4 +/- 4.5 vs. 0.4 +/- 2.0, P = 0.03). MMs were not correlated with age, tremor duration, or severity and were most severe in cases with rest tremor. Thus, it was concluded that MM occurred in 1/3 of ET cases. These results further expand the spectrum of nontremor, motor phenomenology seen in ET. Whether, as in PD, MMs in ET represent a failure of subcortical structures to support the cortical network involved with the initiation of unilateral motor activity, requires future neurophysiological investigation.

The Bereitschaftspotential in essential tremor

OBJECTIVE

Essential tremor (ET) is an involuntary postural oscillation. It is unclear to which extent motor cortical activity in preparation of volitional movement is abnormal in ET. We measured the Bereitschaftspotential (BP) to address this question.

METHODS

Given the known influence of the cerebello-dentato-thalamo-cortical projection in the generation of the BP, patients were divided into two groups, defined by purely postural tremor (ET(PT)) or additional presence of intention tremor (ET(IT)) and compared to healthy controls. BP was recorded during self-paced rapid wrist extension movements.

RESULTS

The late BP (500-0 ms before movement onset) was increased over the mid-frontal area in ET(PT), whereas it was reduced over the mid-parietal area in ET(IT) when compared to healthy controls. In addition, the late BP was reduced over a widespread centro-parietal area in ET(IT) compared to ET(PT).

CONCLUSIONS

Findings suggest that presence vs. absence of cerebellar signs (intention tremor) in ET results in differential affection of volitional preparatory motor cortical activity. The BP increase in ET(PT) may indicate compensatory activity, whereas the widespread centro-parietal BP reduction in ET(IT) suggests dysfunction of the cerebello-dentato-thalamo-cortical projection.

SIGNIFICANCE

Reduction of the late BP amplitude may serve as a surrogate marker for dysfunction of the cerebello-dentato-thalamo-cortical projection in ET.

Control of a neuroprosthesis for grasping using off-line classification of electrocorticographic signals: case study

STUDY DESIGN

Proof of concept study to control a neuroprosthesis for grasping using identification of arm movements from ECoG signals.

OBJECTIVE

To test the feasibility of using electrocorticographic (ECoG) signals as a control method for a neuroprosthesis for grasping.

SETTING

Acute care hospital, Toronto Western Hospital and spinal cord injury (SCI) rehabilitation centre, Toronto Rehabilitation Institute, Lyndhurst Centre. Both hospitals are located in Toronto, Canada.

METHODS

Two subjects participated in this study. The first subject had subdural electrodes implanted on the motor cortex for the treatment of essential tremor (ET). ECoG signals were recorded while the subject performed specific arm movements. The second subject had a complete SCI at C6 level (ASIA B score) and was fitted with a neuroprosthesis, capable of identifying arm movements from ECoG signals off-line, for grasping. To operate the neuroprosthesis, subject 2 issued a command that would trigger the release of a randomly selected ECoG signal recorded from subject 1, associated with a particular arm movement. The neuroprosthesis identified which arm movement was performed at the time of recording and used that information to trigger the stimulation sequence. A correct ECoG classification resulted in the neuroprosthesis producing the correct hand function (that is grasp and release).

RESULTS

The neuroprosthesis classified ECoG signals correctly delivering the correct stimulation strategy with 94.5% accuracy.

CONCLUSIONS

The feasibility of using ECoG signals as a control strategy for a neuroprosthesis for grasping was shown.