During visually guided reaching, proximal limb muscles can be activated within 80 ms of target appearance. Such 'express' visuomotor responses are temporally aligned with target appearance rather than movement onset, and invariably tuned towards the direction of the visual target regardless of the instructed reach direction. These features prompt the hypothesis that express visuomotor responses are driven by a subcortical pathway. We tested this by measuring the changes in Motor Evoked Potentials (MEPs) following Transcranial Magnetic Stimulation (TMS) or Transcranial Electrical Stimulation (TES) of the motor cortex as participants reached either towards or away from visual targets. We found that 70-80 ms after target presentation, MEPs in primary shoulder flexor muscle (pectoralis major) were oriented towards the target direction regardless of whether the participant subsequently reached towards or away from the target. Similar target-oriented MEP modulations were seen in posterior deltoid and biceps brachii, whereas MEPs in a finger muscle were affected neither by target nor reach direction. Critically, there were no significant differences in modulation of responses to TMS and TES across all reaching conditions, which suggests that the target-oriented modulation occurs downstream of the motor cortex output neurons. Combined, our results show that rapid target-oriented corticospinal excitability changes are tuned to the location of the visual target and at least partly driven by a subcortical pathway. A prime candidate for such subcortical modulation involves the superior colliculus and reticular formation.

Autism Spectrum Disorder results in deficit in social interaction, non-verbal communication and social reciprocity. Cognitive tasks pertaining to emotion processing are often preferred to distinguish the ASD children from the typically developing ones. We analysed the role of face and emotion processing in ASD and explored the feasibility of using EEG as a neural marker for detecting ASD. Subjects performed a visual perceptual task with face and nonface stimuli. Successful ASD detection was possible as early as 50 ms. post stimulus onset. Alpha and Beta oscillations seem to best identify autistic individuals. Multivariate pattern analysis and source localization studies points to the role of early visual processing and attention rather than emotion and face processing in detecting autism.

The dynamics of muscle activation during fast visually guided reaching are suggestive of two neural control signals; an early signal that acts at 'express' latencies in response to the visual stimulus, and a longer latency signal that executes a strategic reach plan. Here we developed a task designed to temporally isolate the express visuomotor response from the longer latency muscle response, and to characterize the time course of corticospinal excitability changes in the express response time window when the late voluntary response is delayed. We tested this by measuring electromyograms (EMG) and changes in Motor Evoked Potential (MEP) amplitudes following Transcranial Magnetic Stimulation (TMS) of the motor cortex, as participants reached either towards or away from visual targets. Crucially, the information about the task rule was provided by the luminance of the target itself, and so was unknown to the subject until the instant of target presentation. This feature delayed reaction times, likely because additional (presumably cortical) processing was required to interpret and apply the rule before formation of a goal directed reach plan. The earliest EMG responses to target presentation occurred with a 70-105 ms time window, and were oriented to bring the hand toward the location of the target. However, there was also a slightly later response that was also time-locked to target appearance in a 105-140 ms time window. This second response was 'reciprocal' to the first, such that it was oriented to take the hand in the direction opposite from the target. In some participants, additional oscillating cycles were apparent after the first two target-related responses. These multiphasic express visuomotor responses were nearly identical in both pro- and anti-reach conditions. These muscle activity responses were generally reflected in the temporal pattern of corticospinal excitability modulations in experiment two. Indeed, the MEP and background EMG responses showed an alternating pattern similar to that in experiment one, although the effect was clearer in the anti-reach than the pro-reach condition. Overall, the data show that the express and voluntary responses are indeed distinct neural control signals, which supports the hypothesis that at least two separate neural pathways (one slow and one fast) contribute to the control of visually guided reaching. The properties of the fast pathway are consistent with a tecto-reticulospinal pathway, while those of the slow pathway are consistent with a transcortical loop.