Search

We have investigated the effects of mental set on predictive capabilities using a saccade square-wave tracking paradigm with ten normal subjects, comparing three amplitudes (10, 20, and 40°) and five inter-stimulus intervals (ISIs) (400, 500, 625, 1000, and 2000 ms). Subjects were instructed simply to "follow the lights" (passive, reflexive instruction) or explicitly "move your eyes in time with the lights" (active, volitional instruction). Saccades were defined as reflexive (latency>100 ms), predictive (- 200 ms < latency < 100 ms), or anticipatory (latency < - 200 ms). We also calculated arrival time (saccade latency + saccade duration). Instructions had a striking effect on predictive performance. The effects were greatest with the longest ISIs (1000 and 2000 ms) and the largest target displacement (40°). With the active instruction there were more predictive and anticipatory saccades and with the passive instruction more reflexive saccades. Furthermore, with the active instruction subjects could take into account the duration of the impending saccade so that the eyes would arrive closer to the appearance of the target no matter what the amplitude of the required saccade. In sum, cognitive set, as determined by the specific instructions given to the subject, has a striking effect on predictive saccade behavior, which has important implications for interpreting physiological and imaging correlates of predictive behavior in normals and in patients with neurological disease. [ABSTRACT FROM AUTHOR]

Abstract: Objective: To characterise the activation of the contra- and ipsilateral primary somatosensory cortex (SI) after tactile stimulation of the face. Methods: Trigeminal somatosensory evoked magnetic fields (TSEFs) were recorded after tactile stimulation of the lower lip, cheek, chin and forehead in 11 healthy subjects. The responses were determined visually from the waveforms and modelled with equivalent current dipoles (ECDs). Results: Contralateral SI responses were evoked in all subjects after lip stimulation, and in 91% and 64% after right and left cheek, 73% and 82% after chin and 64% and 27% after forehead stimulation. The responses usually showed an early double-peak wave pattern, the underlying sources localising to the SI. In addition, altogether 37 ipsilateral SI responses were evoked in eight subjects. Fourteen of these responses were amenable to ECD modelling and localised to ipsilateral SI. Conclusions: Tactile stimulation of the lip area reliably activates the contralateral SI in normal subjects, but the success rate for other trigeminal areas is lower. Ipsilateral responses can be present after stimulation of any of the trigeminal branches in normal subjects. Significance: Recording of TSEFs after tactile stimulation of particularly the lip area provides a non-invasive technique to study the function of the trigeminal nerve. [Copyright &y& Elsevier]