Kai V. Thilo

Transcranial magnetic stimulation of medial–frontal cortex impairs the processing of angry facial expressions

Growing evidence suggests that the recognition of different emotional states involves at least partly separable neural circuits. Here we assessed the discrimination of both anger and happiness in healthy subjects receiving transcranial magnetic stimulation (TMS) over the medial–frontal cortex or over a control site (mid-line parietal cortex). We found that TMS over the medial–frontal cortex impairs the processing of angry, but not happy, facial expressions of emotion.

The site of saccadic suppression

During rapid eye movements, or saccades, stable vision is maintained by active reduction of visual sensitivity. The site of this saccadic suppression remains uncertain. Here we show that phosphenes—small illusory visual perceptions—induced by transcranial magnetic stimulation (TMS) to the human occipital cortex are immune to saccadic suppression, whereas phosphenes induced by retinal stimulation are not, thus providing direct physiological evidence that saccadic suppression occurs between the retina and the occipital visual cortex.

Spatial Attention Changes Excitability of Human Visual Cortex to Direct Stimulation

Summary Conscious perception depends not only on sensory input, but also on attention [1, 2]. Recent studies in monkeys [3–6] and humans [7–12] suggest that influences of spatial attention on visual awareness may reflect top-down influences on excitability of visual cortex. Here we tested this specifically, by providing direct input into human visual cortex via cortical transcranial magnetic stimulation (TMS) to produce illusory visual percepts, called phosphenes. We found that a lower TMS intensity was needed to elicit a conscious phosphene when its apparent spatial location was attended, rather than unattended. Our results indicate that spatial attention can enhance visual-cortex excitability, and visual awareness, even when sensory signals from the eye via the thalamic pathway are bypassed.

Repetitive transcranial magnetic stimulation for Tourette syndrome

In a single-blinded, placebo-controlled, crossover repetitive transcranial magnetic stimulation (rTMS) trial, 16 patients with Gilles de la Tourette syndrome (GTS) received in random sequence 1 Hz motor, premotor, and sham rTMS, which each consisted of two 20-minute rTMS sessions applied on 2 consecutive days. In the 12 patients who completed the trial, there was no significant improvement of symptoms after any of the rTMS conditions as assessed with the Motor tic, Obsessions and compulsions, Vocal tic Evaluation Survey.

Phosphene threshold as a function of contrast of external visual stimuli

Transcranial magnetic stimulation (TMS) of the occipital lobe is frequently used to induce visual percepts by direct stimulation of visual cortex. The threshold magnetic field strength necessary to elicit a visual percept is often regarded as a measure of electrical excitability of visual cortex. Using single-pulse TMS during visual motion stimulus presentation, we investigated the relationship between different degrees of visual cortical preactivation and cortical phosphene threshold (PT). The two possible, mutually exclusive, predictions on the outcome of this experiment were that a) PT increases with stronger preactivation because of a decrease in the signal-to-noise ratio, or b) that PT decreases with increased preactivation because of the increase in neuronal response towards some threshold. PTs for single-pulse stimulation of the occipital lobe were determined for eight subjects while they passively viewed a horizontally drifting luminance-modulated sinewave grating. Gratings used were of four different luminance contrasts while the spatial and temporal frequencies remained constant. PTs were shown to increase significantly as the background grating increased in contrast. These results suggest that the neural activity underlying the perception of a phosphene can be considered a type of signal that can be partially masked by another signal, in this case the visual cortical activation produced by passive viewing of drifting gratings.

Chronostasis without voluntary action

In a previous study we explored auditory chronostasis and suggested an arousal account of this temporal illusion rather than one dependent on backdating actions to the onset of a motor event. Here we present three experiments designed to distinguish between two competing accounts of the mechanisms underlying the illusion. Experiment 1 investigated whether voluntary movements are necessary for the illusion to occur. Experiment 2 sought to clarify whether auditory chronostasis occurs when the intervals to be judged are continuous (temporally contiguous) rather than separate events. Experiment 3 was designed to establish whether increased task demands account for the illusion. Together the results from these experiments show that chronostasis is an illusion that is not dependent on voluntary action, can occur without a change in the spatial location of the stimulus (thus precluding an account based on spatial attention), occurs with discrete as well as continuous events, and is affected by the salience of the termination of the event to be timed rather than the onset. Collectively these findings suggest that the mechanisms underlying chronostasis are best explained by an arousal hypothesis since neither attention nor backdating to action can account for the commonalities between chronostasis in the auditory, visual and tactile domains.

Vision: When The Clock Appears to Stop

Eye movements produce a temporary loss of visual sensitivity known as saccadic suppression, and a distortion of space perception known as saccadic compression. A new study has reported a seemingly related phenomenon --chronostasis---in which ones perception of time also undergoes an illusory distortion during rapid movements of the eyes.