Effect of an attentional strategy on movement-related potentials recorded from subjects with Huntington's disease

Abnormal Electrophysiological Motor Responses in Huntington's Disease: Evidence of Premanifest Compensation

Background

Huntington's disease (HD) causes progressive motor dysfunction through characteristic atrophy. Changes to neural structure begin in premanifest stages yet individuals are able to maintain a high degree of function, suggesting involvement of supportive processing during motor performance. Electroencephalography (EEG) enables the investigation of subtle impairments at the neuronal level, and possible compensatory strategies, by examining differential activation patterns. We aimed to use EEG to investigate neural motor processing (via the Readiness Potential; RP), premotor processing and sensorimotor integration (Contingent Negative Variation; CNV) during simple motor performance in HD.

Methods

We assessed neural activity associated with motor preparation and processing in 20 premanifest (pre-HD), 14 symptomatic HD (symp-HD), and 17 healthy controls. Participants performed sequential tapping within two experimental paradigms (simple tapping; Go/No-Go). RP and CNV potentials were calculated separately for each group.

Results

Motor components and behavioural measures did not distinguish pre-HD from controls. Compared to controls and pre-HD, symp-HD demonstrated significantly reduced relative amplitude and latency of the RP, whereas controls and pre-HD did not differ. However, early CNV was found to significantly differ between control and pre-HD groups, due to enhanced early CNV in pre-HD.

Conclusions

For the first time, we provide evidence of atypical activation during preparatory processing in pre-HD. The increased activation during this early stage of the disease may reflect ancillary processing in the form of recruitment of additional neural resources for adequate motor preparation, despite atrophic disruption to structure and circuitry. We propose an early adaptive compensation mechanism in pre-HD during motor preparation.

The detection and measurement of locomotor deficits in a transgenic mouse model of Huntington's disease are task- and protocol-dependent: influence of non-motor factors on locomotor function

Locomotor performance of transgenic R6/2 mice carrying the Huntington's disease (HD) mutation was assessed using four different tasks, fixed speed rotarod, accelerating rotarod, Digigait and footprint test. The tasks were compared directly in age- and CAG repeat-matched R6/2 mice. Accelerating rotarod was more sensitive than fixed speed rotarod for detecting early motor deficits in R6/2 mice. The sensitivity of accelerating rotarod increased with the acceleration rate and/or the start speed from which the rod accelerated. Differences between tasks were not due to inability of R6/2 mice to maintain balance at high speeds or increased fatigue on accelerating rotarod, but to difficulties in coordinating gait changes required by the constant change in speed on accelerating rotarod. The footprint test was sensitive to gait disturbances. However, surprisingly, R6/2 mice did not show major gait abnormalities on an automated treadmill task (Digigait), even though they showed overt gait deficits in the home cage. The fact that the sensitivity for detecting motor deficits depended strongly on the individual task, and on the protocol used, suggests that non-motor factors were differentially engaged in the different paradigms. We thus recommend that more than one task should be used for detecting and tracking different aspects of motor decay in animal models of HD. Since deficits in non-motor factors such as executive function and motivation may differentially influence motor outcome in each task, our results call for a more thorough investigation of the importance of higher level control of locomotion in animal models of HD.