The cerebellum is implicated in the control of saccade but saccade abnormality in cerebellar disorders is not fully delineated, especially in the vertical directions. To clarify the role of the ...cerebellum, we studied saccades in hereditary spinocerebellar degeneration (SCD) with pure cerebellar presentation.
Subjects were 20 SCD patients (SCA6, 31) and 19 normal age-matched controls. We used the visual guided (VGS) and memory guided saccade tasks (MGS) in which targets were presented in 8 possible directions with 45 degree separation, and recorded saccades with a video-based eye tracker.
In SCA patients, latency was significantly delayed mainly in vertical and oblique directions, which correlated with SARA scores. The number of both overshoot and undershoot increased correlatively with SARA scores in all directions. Peak velocity showed no change, but the time from the beginning to the peak velocity of the saccade was shorter, whereas the time from the peak velocity to the end of saccade was longer.
The change in amplitude and velocity profile may reflect abnormal output from the cerebellar nuclei, whereas the pathophysiology of prolonged latency remains elusive. We hope the saccade analysis paves the way toward objective assessment of SCD and other neurological disorders.
Gaze and hand movements are known to be closely linked in daily actions (eye-hand coordination), and the cerebellum is implicated in the control of this eye-hand coordination. There are negative ...reciprocal interactions between the eye and hand movements when patients with cerebellar dysfunction perform a target tracking task. We devised a system which is capable of simultaneously recording the trajectory of hand and eye movements when subjects performed a visually guided reaching task. The aim of this preliminary study was to investigate how cerebellar dysfunction affects the coordination.
Subjects were 8 patients with hereditary spinocerebellar degeneration (SCA6 or SCA31) with pure cerebellar symptoms and 9 age-matched normal controls. A video-based eye tracker recorded eye movements while a touch panel recorded the trajectory of finger movements while performing the visually guided reaching task. A fixation spot was presented in the center of the touch panel, which the subjects fixated and touched with the index finger. At a random interval, this fixation spot moved to a peripheral position, selected from positions at an eccentricity of 10 or 20 degrees (in 8 directions separated by 45 degrees), to which the subjects were to move their fingers by sliding their fingers over the monitor. The subjects also performed a visual guided saccade task, in which they made a saccade to the peripheral target without moving the finger.
In SCA patients, trajectory of both eye and finger showed hypermetria in comparison with normal controls. Superimposed trajectories of saccades showed a wider distribution than that of finger movements, which implied that the variability of eye movements did not directly translate into that of the hand movements. In most trials, the eyes preceded the finger movements to the target location, and was locked at the target location until the hand was reached the target location. The interval between onsets of the hand and eye movements was larger for SCA patient than for normal subjects. This wider separation between the hand and eye onset was due to the eyes moving to the targets in multiple steps of saccades with changing direction and the hand did not start before the eyes reached the vicinity of the target.
Eye-hand coordination was disrupted in hereditary spinocerebellar degeneration. In SCA patients, the multistep saccade and saccades that changed direction toward the target prevented gaze locking at the target required for eye-hand coordination, and led to increased interval between the saccade onset and finger onset.
Autism spectrum disorder (ASD) presents certain hallmark features associated with cognitive and social functions, however, the ability to estimate self-generated distance and duration in individuals ...with ASD are unclear. We compared the performance of 20 ASD individuals with 20 typical developments (TDs) with respect to two tasks: (1) the drawing of a line of a specified distance (10 or 20 cm) and (2) waiting for a specified time (10 or 20 s). We observed that both the line distances and waiting times were substantially shorter in the ASD group than in the TD group. Furthermore, a trait of "attention to detail," as measured by the Autism-Spectrum Quotient, correlated with some distance and duration productions observed in individuals with ASD. We suggest that attentional functions are related to the contraction of distance and duration in ASD.
Corpus callosum connects the bilateral primary motor cortices (M1s) and plays an important role in motor control. Using the paired-pulse transcranial magnetic stimulation (TMS) paradigm, we can ...measure interhemispheric inhibition (IHI) and interhemispheric facilitation (IHF) as indexes of the interhemispheric interactions in humans. We investigated how quadripulse transcranial magnetic stimulation (QPS), one form of repetitive TMS (rTMS), on M1 affects the contralateral M1 and the interhemispheric interactions. QPS is able to induce bidirectional plastic changes in M1 depending on the interstimulus intervals (ISIs) of TMS pulses: long-term potentiation (LTP)-like effect by QPS-5 protocol, and long-term depression-like effect by QPS-50, whose numbers indicate the ISI (ms). Twelve healthy subjects were enrolled. We applied QPS over the left M1 and recorded several parameters before and 30 min after QPS. QPS-5, which increased motor-evoked potentials (MEPs) induced by left M1 activation, also increased MEPs induced by right M1 activation. Meanwhile, QPS-50, which decreased MEPs elicited by left M1 activation, did not induce any significant changes in MEPs elicited by right M1 activation. None of the resting motor threshold, active motor threshold, short-interval intracortical inhibition, long-interval intracortical inhibition, intracortical facilitation, and short-interval intracortical inhibition in right M1 were affected by QPS. IHI and IHF from left to right M1 significantly increased after left M1 QPS-5. The degree of left first dorsal interosseous MEP amplitude change by QPS-5 significantly correlated with the degree of IHF change. We suppose that the LTP-like effect on the contralateral M1 may be produced by some interhemispheric interactions through the corpus callosum.
We studied the role of gaze in performing the trail-making test (TMT) in eight normal subjects, a task frequently used to assess frontal executive function in neurological patients. TMT was presented ...on a touch-panel monitor placed in front of the subjects, on which they were asked to connect the presented numbers with their fingers in an ascending order (version A), or with the added task of alternately connecting between the numbers and letters in ascending and alphabetical orders (version B), respectively. The subjects’ gaze position on the monitor was recorded by a video-based eye tracking system (Eyelink 1000), as was the hand (finger) position on the touch-panel. The completion time and the total number of saccades made during the task, the amplitude, peak velocity of saccades and the interval between consecutive saccades (i.e., fixation duration) were measured. Multiple regression analysis showed that the task completion time correlated with the total number of saccades and, less prominently, with the mean fixation duration, suggesting that gaze plays an important role in performing TMT, and should be considered when using this task to assess executive function in neurological patients with eye movement disorders.
The cerebellum is implicated in the control of saccadic eye movement but it is unknown how it differs for vertical and horizontal saccades, since vertical saccades have been rarely studied. To ...clarify the role of the cerebellum we studied saccades in hereditary spinocerebellar degeneration in two dimensional directions.
We compared saccade performance in 16 patients (SCA31 and SCA6) with that in 19 normal age-matched controls. We used the visual guided (VGS) and memory guided tasks (MGS) in which targets were presented in eight directions with 45 degrees separation, and recorded saccades with a video-based eye tracker.
In SCA patients, latency of VGS was significantly delayed compared with normal subjects in vertical and oblique directions, which correlated with SARA scores. MGS latency was significantly delayed only in the oblique direction. Hypermetria was prominently detected in the vertical and oblique directions, but less in the horizontal directions.
Abnormal latency and dysmetria are easily detected for directions having vertical component. The cerebellum may be more involved in vertical than in horizontal saccade system, or vertical saccade system may be more susceptible to diseases than horizontal saccades. Further study of other diseases will be helpful to differentiate between these possibilities.
The supplementary motor area (SMA) is a secondary motor area that is involved in various complex hand movements. In animal studies, short latency and probably direct excitatory inputs from SMA to the ...primary motor cortex (M1) have been established. Although human imaging studies revealed functional connectivity between SMA and M1, its electrophysiological nature has been less studied. This study explored the connection between SMA and M1 in humans using a single-pulse transcranial magnetic stimulation (TMS) over SMA. First, TMS over SMA did not alter the corticospinal tract excitability measured by the size of motor evoked potential elicited by single-pulse TMS over M1. Next, we measured short-interval intracortical facilitation (SICF), which reflects the function of a facilitatory circuit within M1, with or without a single-pulse TMS over SMA. When the intensity of the second pulse in the SICF paradigm (S2) was as weak as 1.0 active motor threshold for a hand muscle, SMA stimulation significantly enhanced the SICF. Furthermore, this enhancement by SMA stimulation was spatially confined and had a limited time window. On the other hand, SMA stimulation did not alter short-interval intracortical inhibition or contralateral silent period duration, which reflects the function of an inhibitory circuit mediated by gamma-aminobutyric acid A (GABA
A
) or GABA
B
receptors, respectively. We conclude that a single-pulse TMS over SMA modulates a facilitatory circuit within M1.
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