Early visual cortex reflects initiation and maintenance of task set

Individual variability in brain representations of pain

Characterizing cerebral contributions to individual variability in pain processing is crucial for personalized pain medicine, but has yet to be done. In the present study, we address this problem by identifying brain regions with high versus low interindividual variability in their relationship with pain. We trained idiographic pain-predictive models with 13 single-trial functional MRI datasets (n = 404, discovery set) and quantified voxel-level importance for individualized pain prediction. With 21 regions identified as important pain predictors, we examined the interindividual variability of local pain-predictive weights in these regions. Higher-order transmodal regions, such as ventromedial and ventrolateral prefrontal cortices, showed larger individual variability, whereas unimodal regions, such as somatomotor cortices, showed more stable pain representations across individuals. We replicated this result in an independent dataset (n = 124). Overall, our study identifies cerebral sources of individual differences in pain processing, providing potential targets for personalized assessment and treatment of pain.

Task-related activity in human visual cortex

The brain exhibits widespread endogenous responses in the absence of visual stimuli, even at the earliest stages of visual cortical processing. Such responses have been studied in monkeys using optical imaging with a limited field of view over visual cortex. Here, we used functional MRI (fMRI) in human participants to study the link between arousal and endogenous responses in visual cortex. The response that we observed was tightly entrained to task timing, was spatially extensive, and was independent of visual stimulation. We found that this response follows dynamics similar to that of pupil size and heart rate, suggesting that task-related activity is related to arousal. Finally, we found that higher reward increased response amplitude while decreasing its trial-to-trial variability (i.e., the noise). Computational simulations suggest that increased temporal precision underlies both of these observations. Our findings are consistent with optical imaging studies in monkeys and support the notion that arousal increases precision of neural activity.

The brain exhibits widespread endogenous responses in the absence of visual stimuli, even at the earliest stages of visual cortical processing. This fMRI study characterizes a widespread hemodynamic response in early visual cortex that is not related to visual input but instead reflects a participant’s engagement in a task, is modulated by expected monetary reward, and may reflect neural quenching.

Background connectivity between frontal and sensory cortex depends on task state, independent of stimulus modality

The human brain has the ability to process identical information differently depending on the task. In order to perform a given task, the brain must select and react to the appropriate stimuli while ignoring other irrelevant stimuli. The dynamic nature of environmental stimuli and behavioral intentions requires an equally dynamic set of responses within the brain. Collectively, these responses act to set up and maintain states needed to perform a given task. However, the mechanisms that allow for setting up and maintaining a task state are not fully understood. Prior evidence suggests that one possible mechanism for maintaining a task state may be through altering 'background connectivity,' connectivity that exists independently of the trials of a task. Although previous studies have suggested that background connectivity contributes to a task state, these studies have typically not controlled for stimulus characteristics, or have focused primarily on relationships among areas involved with visual sensory processing. In the present study we examined background connectivity during tasks involving both visual and auditory stimuli. We examined the connectivity profiles of both visual and auditory sensory cortex that allow for selection of task-relevant stimuli, demonstrating the existence of a potentially universal pattern of background connectivity underlying attention to a stimulus. Participants were presented with simultaneous auditory and visual stimuli and were instructed to respond to only one, while ignoring the other. Using functional MRI, we observed task-based modulation of the background connectivity profile for both the auditory and visual cortex to certain brain regions. There was an increase in background connectivity between the task-relevant sensory cortex and control areas in the frontal cortex. This increase in synchrony when receiving the task-relevant stimulus as compared to the task irrelevant stimulus may be maintaining paths for passing information within the cortex. These task-based modulations of connectivity occur independently of stimuli and could be one way the brain sets up and maintains a task state.

Transient human auditory cortex activation during volitional attention shifting

While strong activation of auditory cortex is generally found for exogenous orienting of attention, endogenous, intra-modal shifting of auditory attention has not yet been demonstrated to evoke transient activation of the auditory cortex. Here, we used fMRI to test if endogenous shifting of attention is also associated with transient activation of the auditory cortex. In contrast to previous studies, attention shifts were completely self-initiated and not cued by transient auditory or visual stimuli. Stimuli were two dichotic, continuous streams of tones, whose perceptual grouping was not ambiguous. Participants were instructed to continuously focus on one of the streams and switch between the two after a while, indicating the time and direction of each attentional shift by pressing one of two response buttons. The BOLD response around the time of the button presses revealed robust activation of the auditory cortex, along with activation of a distributed task network. To test if the transient auditory cortex activation was specifically related to auditory orienting, a self-paced motor task was added, where participants were instructed to ignore the auditory stimulation while they pressed the response buttons in alternation and at a similar pace. Results showed that attentional orienting produced stronger activity in auditory cortex, but auditory cortex activation was also observed for button presses without focused attention to the auditory stimulus. The response related to attention shifting was stronger contralateral to the side where attention was shifted to. Contralateral-dominant activation was also observed in dorsal parietal cortex areas, confirming previous observations for auditory attention shifting in studies that used auditory cues.

Retinotopic patterns of functional connectivity between V1 and large-scale brain networks during resting fixation

Psychophysical and neurobiological evidence suggests that central and peripheral vision are specialized for different functions. This specialization of function might be expected to lead to differences in the large-scale functional interactions of early cortical areas that represent central and peripheral visual space. Here, we characterize differences in whole-brain functional connectivity among sectors in primary visual cortex (V1) corresponding to central, near-peripheral, and far-peripheral vision during resting fixation. Importantly, our analyses reveal that eccentricity sectors in V1 have different functional connectivity with non-visual areas associated with large-scale brain networks. Regions associated with the fronto-parietal control network are most strongly connected with central sectors of V1, regions associated with the cingulo-opercular control network are most strongly connected with near-peripheral sectors of V1, and regions associated with the default mode and auditory networks are most strongly connected with far-peripheral sectors of V1. Additional analyses suggest that similar patterns are present during eyes-closed rest. These results suggest that different types of visual information may be prioritized by large-scale brain networks with distinct functional profiles, and provide insights into how the small-scale functional specialization within early visual regions such as V1 relates to the large-scale organization of functionally distinct whole-brain networks.

Modulation of cognitive control levels via manipulation of saccade trial-type probability assessed with event-related BOLD fMRI

Cognitive control supports flexible behavior adapted to meet current goals and can be modeled through investigation of saccade tasks with varying cognitive demands. Basic prosaccades (rapid glances toward a newly appearing stimulus) are supported by neural circuitry, including occipital and posterior parietal cortex, frontal and supplementary eye fields, and basal ganglia. These trials can be contrasted with complex antisaccades (glances toward the mirror image location of a stimulus), which are characterized by greater functional magnetic resonance imaging (MRI) blood oxygenation level-dependent (BOLD) signal in the aforementioned regions and recruitment of additional regions such as dorsolateral prefrontal cortex. The current study manipulated the cognitive demands of these saccade tasks by presenting three rapid event-related runs of mixed saccades with a varying probability of antisaccade vs. prosaccade trials (25, 50, or 75%). Behavioral results showed an effect of trial-type probability on reaction time, with slower responses in runs with a high antisaccade probability. Imaging results exhibited an effect of probability in bilateral pre- and postcentral gyrus, bilateral superior temporal gyrus, and medial frontal gyrus. Additionally, the interaction between saccade trial type and probability revealed a strong probability effect for prosaccade trials, showing a linear increase in activation parallel to antisaccade probability in bilateral temporal/occipital, posterior parietal, medial frontal, and lateral prefrontal cortex. In contrast, antisaccade trials showed elevated activation across all runs. Overall, this study demonstrated that improbable performance of a typically simple prosaccade task led to augmented BOLD signal to support changing cognitive control demands, resulting in activation levels similar to the more complex antisaccade task.

Distinct effects of trial-driven and task Set-related control in primary visual cortex

Task sets are task-specific configurations of cognitive processes that facilitate task-appropriate reactions to stimuli. While it is established that the trial-by-trial deployment of visual attention to expected stimuli influences neural responses in primary visual cortex (V1) in a retinotopically specific manner, it is not clear whether the mechanisms that help maintain a task set over many trials also operate with similar retinotopic specificity. Here, we address this question by using BOLD fMRI to characterize how portions of V1 that are specialized for different eccentricities respond during distinct components of an attention-demanding discrimination task: cue-driven preparation for a trial, trial-driven processing, task-initiation at the beginning of a block of trials, and task-maintenance throughout a block of trials. Tasks required either unimodal attention to an auditory or a visual stimulus or selective intermodal attention to the visual or auditory component of simultaneously presented visual and auditory stimuli. We found that while the retinotopic patterns of trial-driven and cue-driven activity depended on the attended stimulus, the retinotopic patterns of task-initiation and task-maintenance activity did not. Further, only the retinotopic patterns of trial-driven activity were found to depend on the presence of inter-modal distraction. Participants who performed well on the intermodal selective attention tasks showed strong task-specific modulations of both trial-driven and task-maintenance activity. Importantly, task-related modulations of trial-driven and task-maintenance activity were in opposite directions. Together, these results confirm that there are (at least) two different processes for top-down control of V1: One, working trial-by-trial, differently modulates activity across different eccentricity sectors - portions of V1 corresponding to different visual eccentricities. The second process works across longer epochs of task performance, and does not differ among eccentricity sectors. These results are discussed in the context of previous literature examining top-down control of visual cortical areas.

Retinotopic patterns of background connectivity between V1 and fronto-parietal cortex are modulated by task demands

Attention facilitates the processing of task-relevant visual information and suppresses interference from task-irrelevant information. Modulations of neural activity in visual cortex depend on attention, and likely result from signals originating in fronto-parietal and cingulo-opercular regions of cortex. Here, we tested the hypothesis that attentional facilitation of visual processing is accomplished in part by changes in how brain networks involved in attentional control interact with sectors of V1 that represent different retinal eccentricities. We measured the strength of background connectivity between fronto-parietal and cingulo-opercular regions with different eccentricity sectors in V1 using functional MRI data that were collected while participants performed tasks involving attention to either a centrally presented visual stimulus or a simultaneously presented auditory stimulus. We found that when the visual stimulus was attended, background connectivity between V1 and the left frontal eye fields (FEF), left intraparietal sulcus (IPS), and right IPS varied strongly across different eccentricity sectors in V1 so that foveal sectors were more strongly connected than peripheral sectors. This retinotopic gradient was weaker when the visual stimulus was ignored, indicating that it was driven by attentional effects. Greater task-driven differences between foveal and peripheral sectors in background connectivity to these regions were associated with better performance on the visual task and faster response times on correct trials. These findings are consistent with the notion that attention drives the configuration of task-specific functional pathways that enable the prioritized processing of task-relevant visual information, and show that the prioritization of visual information by attentional processes may be encoded in the retinotopic gradient of connectivty between V1 and fronto-parietal regions.