Boris Burle

The dual nature of time preparation: neural activation and suppression revealed by transcranial magnetic stimulation of the motor cortex

Single‐pulse transcranial magnetic stimulations (TMSs) of the motor cortex (M1) were performed in order to decipher the neural mechanisms of time preparation. We varied the degree to which it was possible to prepare for the response signal in a choice reaction time (RT) task by employing either a short (500 ms) or a long (2500 ms) foreperiod in separate blocks of trials. Transcranial magnetic stimulations were delivered during these foreperiods in order to study modulations in both the size of the motor evoked potential (MEP) and the duration of the silent period (SP) in tonically activated response agonists. Motor evoked potential area and silent period duration were assumed to reflect, respectively, the excitability of the cortico‐spinal pathway and the recruitment of inhibitory cortical interneurons. Shorter reaction times were observed with the shorter foreperiod, indicating that a better level of preparation was attained for the short foreperiod. Silent period duration decreased as time elapsed during the foreperiod and this decrement was more pronounced for the short foreperiod. This result suggests that time preparation is accompanied by a removal of intracortical inhibition, resulting in an activation. Motor evoked potential area decreased over the course of the short foreperiod, but not over the long foreperiod, revealing that time preparation involves the inhibition of the cortico‐spinal pathway. We propose that cortico‐spinal inhibition secures the development of cortical activation, preventing erroneous premature responding.

What’s an internal clock for?: From temporal information processing to temporal processing of information

The existence of an internal clock and its involvement in information processing has been investigated in humans using the experimental protocol of Treisman et al. (1990) [Treisman et al., 1990. Perception, 19, 705-743]. In this protocol, a periodical stimulation, which is assumed to drive an internal clock, is delivered during a reaction time (RT) task. The accelerating or slowing down effects of the periodical stimulation, according to its frequency, allowed an estimate to be made of a simple harmonic of the frequency of the internal clock. The estimate was close to 21 Hz. In the framework of the serial model of information processing, the present work investigates the involvement of the internal clock in the transmission of information between processing stages during RT. The data tend to support the idea that the internal clock allows the transfer of information from one stage to the next one at definite moments only, periodically distributed in time. According to our results, and recent data from the literature on electric cortical oscillations, we propose a model of an internal clock sending periodic inhibition, which would permit an increased signal/noise ratio in the processing and the transmission of information in the central nervous system.

Sequential adjustments before and after partial errors.

In choice reaction time tasks, subjects speed up before making an error, but slow down afterward to prevent the occurrence of a new error. In some trials, the correct response is preceded by an incorrect electromyographic (EMG) activation too small to reach the response threshold. In this article, we show that these incorrect EMG activations give rise to the same sequential effects as overt errors: Before a trial containing an incorrect EMG activation, subjects speed up, whereas after that trial, they slow down. These activations reflect errors that have been detected, inhibited, and corrected in time. As such, they index the involvement of online executive control.

Voluntary and involuntary control over automatic processing in spatial congruency tasks: Editors' introduction

What makes an irrelevant stimulus attribute influence the processing of relevant stimulus and response attributes? Are these processes governed by the nature of the attributes and their mutual relationship (bottom-up processes) or are they strategically determined (top-down)? Cognitive psychology has a long tradition of over a century of research on these questions, which pertain to the domain of cognitive control. One of the most fruitful and interesting approaches to the topic of cognitive control has been through the study of congruency tasks. In congruency tasks the relationship between stimulus and response features is systematically varied, so that in some conditions relevant and irrelevant information indicate the same response while in other they lead to conflicting response tendencies. Differences in reaction times (RT) or accuracy measures between conditions with and without conflicting response tendencies are called congruency effects, and have been reported in most areas of cognitive psychology. Congruency effects have been demonstrated in a wide variety of tasks, with different S‐R sets and both within and between different modalities.