Holmes tremor in a patient with progressive multifocal leukoencephalopathy.

BACKGROUND: Progressive multifocal leukencephalopathy (PML) is a rare, sometimes fatal viral disease in patients with primary or secondary immunosuppression. CASE DESCRIPTION: A 57-year-old immunocompetent female with intractable Holmes tremor and elongated unique brainstem lesion reported to our hospital. The cerebrospinal fluid (CSF) screening for John Cunningham virus was negative and the diagnosis was established by brain biopsy. The course was rapidly fatal. CONCLUSION: This atypical presentation of PML in an immunocompetent patient illustrates that diagnosis can be missed without brain biopsy

Influence of time pressure in a simple response task, a choice-by-location task, and the Simon task

Examined the influence of strategy for a simple response task, a choice-by-location task, and the Simon task by varying time pressure in 11 Ss (mean age 28 yrs). Besides reaction time (RT) and accuracy, we measured response force and derived two measures from the event-related EEG potential to form an index for attentional orienting (posterior contralateral negativity: PCN) and the start of motor activation (the lateralized readiness potential: LRP). For the choice-by- location task and the Simon task, effects of time pressure were found on the response-locked LRP, but not on the onset of the PCN and the stimulus-locked LRP. Thus, strategy influences processing after the start of motor activation in choice tasks. A small effect of time pressure was found on the peak latency of the PCN in the Simon task, which suggests that time pressure may affect attentional orienting. In the simple response task, time pressure reduced the amplitude of the PCN. This finding suggests that strategy affects attentional orienting to stimuli when these stimuli are not highly relevant. Finally, the effect of time pressure on RT was much larger in the simple response task than in the other tasks, which may be ascribed to the possibility of preparing the required response in the simple response task

Posterior and anterior contribution of hand-movement preparation to late CNV

The late part of the Contingent Negative Variation (CNV) is assumed to be a composite potential, reflecting both movement preparation and several other processes. To assess the contribution of hand–motor preparation to overall CNV, 3 S1–S2 experiments were performed. Replicating earlier results that have been interpreted as demonstrating hand–motor preparation, Exp 1 showed that CNV gets larger centro–parietally under speed instruction. Exps 2 and 3 compared preparation for hand responses to preparation for ocular responses varying the effector system either between blocks (Exp 2) or between trials (Exp 3) and also comparing these preparation situations to no preparation (Exp 3). Ss consisted of 10 medical students aged 23–29 yrs in Exp 1, 12 Ss aged 23–31 yrs in Exp 2, and 11 Ss in Exp 3. Hand–motor preparation was reflected in CNV getting larger fronto–centrally, with this topography being different from the effect in Exp1. Thus, 2 different kinds of motor preparation appear to be reflected by CNV. One kind may consist of assembling and maintaining the stimulus–response links appropriate to the expected S2 patterns, the other is for activating the hand–motor area. These 2 motor contributions to CNV might reflect the 2 aspects of the parieto–frontal motor system

The influence of time pressure and cue validity on response force in an S1-S2 paradigm

Hypotheses about variations of response force have emphasised the influences of arousal and of motor preparation. To study both types of influences in one experiment, the effects of time pressure and of validity of S1 were investigated in tasks wherein a first stimulus (S1) indicated the most probable response (80% valid) required after a second stimulus (S2). Under time pressure, responses were executed more forcefully while, as could be expected, response times were shorter and errors were more frequent. This pattern of results was not only obtained when time pressure was varied between blocks, but also when varied from trial to trial, by information given by S2. Also invalidly cued responses were executed more forcefully but, as could be expected, in contrast to time pressure, response times were longer and errors were more frequent. The results demonstrate that latency and force of responses may vary in different directions. Ways are outlined on how current hypotheses must be extended in order to account for these results

Lateralized EEG components with direction information for the preparation of saccades versus finger movements

During preparation of horizontal saccades in humans, several lateralized (relative to saccade direction), event-related EEG components occur that have been interpreted as reflecting activity of frontal and parietal eye fields. We investigated to what degree these components are specific to saccade preparation. EEG lateralization was examined within the interval (1 s) between a first (S1) and a second (S2) stimulus, after which a response had to be made (look left or right, or press a button with the left or right index finger). The visual S1 indicated either the direction (left vs right) and/or the effector (eye vs finger), and S2 (visual/auditory in different blocks) added the information not given by S1. An occipital component (220 ms after S1) was effector-independent, probably reflecting processing of the direction code. The following parietotemporal component (320 ms after S1) was specific for direction information. This component seems more relevant for finger movements than for saccades and may reflect a link between visual perception to action. A later frontal component (480 ms after S1) was specific for direction information and may be related to the planning of a lateral movement. One component was entirely specific for the preparation of a finger movement (the lateralized readiness potential before S2). Thus, several different lateralized processes in the S1-S2 interval could be delineated, reflecting hand-specific preparation, processing of the direction code, and the coordination of perception and action, but no components were observed as being specific for saccade preparation