Reward feedback following visual search causes the visual characteristics of targets to become salient and attention-drawing, but little is known about the mechanisms underlying this value-driven capture effect. Here, we use transcranial random noise stimulation (tRNS) to demonstrate that such reward potentiation involves induced plasticity in visual cortex. Human participants completed a feature-search reward-learning task involving the selection of a red or green colored target presented among distractors of various color. Each correct trial garnered reward and the magnitude of reward was determined by the color of the target. Three groups completed this task: two groups received tRNS over either occipital or frontal cortex, and the third group received sham stimulation as a control. In a subsequent test phase of the experiment participants searched for a unique shape presented among colored distractors. During the test phase, no tRNS was applied and no reward was available. However, in some trials a single distractor had color matching that associated with reward during training. Search for the target was impacted by the presence of such reward-associated distractors in the occipital stimulation group, demonstrating that plasticity in visual cortex contributes to value-driven attentional capture.
In experimental settings, most overt behavioral errors are consciously perceived. They are, however, only the tip of the iceberg, and electromyographic recording of the muscles involved in the response reveals subthreshold incorrect response activations. Although they are all efficiently corrected, such "partial errors" are poorly consciously detected. Electroencephalographic recordings (CSD estimate), revealed the sequence of cortical activities that lead, or not, to conscious detection. Besides medioprefrontal activities related to action monitoring and error detection, the motor command sent by the primary motor cortices also differed between detected and undetected partial errors: while it develops identically, it is stopped earlier for the latter than for the former, suggesting a critical role in partial error detection. Second, the analysis of the "Error positivity"-Pe, classically linked to error awareness, confirmed its absence just after partial errors, be they detected or not. However, a Pe occurs after the corrective response of partial errors that were detected, suggesting that we become aware of our partial errors only after their correction. The implication of these results for the link between consciousness and cognitive control are discussed.
Human behavior must be flexible to respond to environmental and social demands, and to achieve these goals, it requires control. For instance, inhibitory control is used to refrain from executing unwanted or anticipated responses to environmental stimuli. When inhibitory mechanisms are inefficient due to some pathological conditions, such as attention-deficit hyperactivity disorder (ADHD) or pathological gambling, patients show a reduced capability of refraining from executing actions. When planning to execute an action, various inhibitory control mechanisms are activated to prevent the unwanted release of impulses and to ensure that the correct response is produced. A great body of research has used various cognitive tasks to isolate one or more components of inhibitory control (e.g., response selectivity) and to investigate their neuronal underpinnings. However, inter-individual differences in behavior are rarely properly considered, although they often represent a considerable source of noise in the data. In the present review, we will address this issue using the specific case of action inhibition, presenting the results of studies that coupled the so-called Go/NoGo paradigm with non-invasive brain stimulation to directly test the effects of motor inhibition on the excitability of the corticospinal system (CSE). Motor preparation is rarely measured in action inhibition studies, and participants’ compliancy to the task’s requests is often assumed rather than tested. Single pulse transcranial magnetic stimulation (TMS) is a powerful tool to directly measure CSE, whose responsivity depends on both excitatory and inhibitory processes. However, when motor preparation is not measured and the task design does not require participants to prepare responses in advance, fluctuations in CSE levels can be mistaken for active inhibition. One way to isolate motor preparation is to use a carefully designed task that allows to control for excessive variability in the timing of activation of inhibitory control mechanisms. Here, we review single pulse TMS studies that have used variants of the Go/NoGo task to investigate inhibitory control functions in healthy participants. We will identify the specific strategies that likely induced motor preparation in participants, and their results will be compared to current theories of action inhibition.
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