Inhibitory motor control — i.e. the ability to suppress unwanted behavioral responses — provides crucial flexibility in goal-directed behavior, allowing individuals to quickly adjust to a changing environment and to overcome pre-potent responses when they are inadequate or inappropriate (see 
for a review). Interest in this topic has dramatically increased over the past several years in accord with the central role of this function in normal human behavior and development, as well as in a range of neurological and psychiatric conditions, such as attention-deficit hyperactivity disorder and substance abuse 
One of the most prominent experimental paradigms designed to investigate response-inhibition capabilities is the Stop-signal task 
. In this task, a choice-reaction Go-stimulus is rapidly followed, on a minority of trials, by a Stop-stimulus requiring participants to withhold the response to the Go-stimulus. Variants of this and related tasks have been used extensively with a variety of methodological approaches to investigate brain processes underlying response inhibition. Converging evidence from these studies has led to the view that a mostly right-hemisphere network of brain areas plays a critical role in response inhibition (but see 
). This network includes the inferior frontal gyrus (IFG; especially the frontal operculum extending into the insula) and the pre-supplementary motor area (pre-SMA), which in turn interacts with the basal ganglia and the thalamus (for reviews see 
Although it is very likely that the loop between the frontal cortex and the basal ganglia/thalamus described above is a core structure subserving response inhibition, it is increasingly recognized that other mechanisms play an important role leading up to response inhibition and in determining whether it will be successful or not. Specifically, it has been reported that selective attention to the task-relevant stimuli can play an important role in determining trial outcome in the Stop-signal task. Numerous studies have reported transient modulations of sensory processing of the relevant stimuli in the time-range of the sensory evoked N1 ERP component, which precedes the implementation of response inhibition, and that these modulations are predictive of the outcome of the process 
. Due to the timing and the posterior topography, such effects can be compellingly attributed to differences in sensory processing, including due to attentional modulations of that processing.
Unfortunately, such conclusions are much more difficult to draw for activity at later time-ranges and in other brain areas, so that a separation of perceptual/attentional processes from those that are directly related to response inhibition has proven difficult. A case in point relates to the right IFG, which has received a lot of experimental support as a key structure in response inhibition. This area is reliably activated in human fMRI studies investigating response inhibition (for a recent comprehensive review, see 
), while lesion and electrophysiological studies in humans have provided corroborating evidence 
. Recent studies, however, have challenged the view that the right IFG is directly involved in response inhibition (but see 
). For example, strong right IFG activations have also been reported in response to other rare stimuli besides task-relevant Stop-stimuli (
, see also 
), consistent with its reported participation in the ventral attention system that has been implicated in bottom-up attentional processes triggered relatively automatically by salient environmental events 
An important distinction in this context that has not yet been established (neither for the right IFG nor for other involved brain areas) is the degree of automaticity with which Stop-trial stimulation elicits neural activity. Specifically, in the existing attention literature it is appreciated that the presentation of rare, and/or physically salient, stimuli (note that Stop-trials meet both criteria) tend to automatically capture attention and activate at least parts of the ventral attention system 
. Such processes can even occur if these stimuli are entirely task-irrelevant (for a recent discussion, see 
). In the context of the Stop-signal task, however, the degree to which neural activity is related to such salience-triggered processes is not clear, versus how much such activation may depend on the general task context, in which the behavioral relevance of stimuli other than Go-stimuli needs to be determined. Establishing such a distinction is important in order to gain insights into which areas and processes are under active top-down control during a Stop-signal task, even if their function is related to control processes that are not directly related to response inhibition. Moreover, because these other functions could also be derailed in psychopathology, thereby potentially mimicking deficits directly in motor control (e.g., 
), disentangling and understanding these processes better is an important goal.
In the present report, we have carried out additional sets of analyses of the data from a recent study 
that included, as a control condition, task-irrelevant Stop-trials from separate task blocks (see ). In our previous report, this control condition was used specifically to subtract out activity related to the sensory processing of Stop-stimuli. Here, we expanded our analyses of these data in order to gauge, on a brain-wide level, the degree to which activity in different brain areas is related to the sensory and attention-attracting features of Stop-stimuli. Additionally, we performed an ROI analyses to investigate the relative degree of activation by Go-trials, task-irrelevant Stop-trials, and task-relevant Stop-trials in key brain areas. These analyses provide activity profiles indicative of separable neural operations that have important implications towards a better understanding of the specific systems-level neural circuits that lead to and implement response inhibition.