The right middle fontal gyrus (MFG) has been proposed to be a site of convergence of the dorsal and ventral attention networks, by serving as a circuit-breaker to interrupt ongoing endogenous attentional processes in the dorsal network and reorient attention to an exogenous stimulus. Here, we probed the contribution of the right MFG to both endogenous and exogenous attention by comparing performance on an orientation discrimination task of a patient with a right MFG resection and a group of healthy controls. On endogenously cued trials, participants were shown a central cue that predicted with 90% accuracy the location of a subsequent peri-threshold Gabor patch stimulus. On exogenously cued trials, a cue appeared briefly at one of two peripheral locations, followed by a variable inter-stimulus interval (ISI; range 0–700 ms) and a Gabor patch in the same or opposite location as the cue. Behavioral data showed that for endogenous, and short ISI exogenous trials, valid cues facilitated responses compared to invalid cues, for both the patient and controls. However, at long ISIs, the patient exhibited difficulty in reverting to top-down attentional control, once the facilitatory effect of the exogenous cue had dissipated. When explicitly cued during long ISIs to attend to both stimulus locations, the patient was able to engage successfully in top-down control. This result indicates that the right MFG may play an important role in reorienting attention from exogenous to endogenous attentional control. Resting state fMRI data revealed that the right superior parietal lobule and right orbitofrontal cortex, showed significantly higher correlations with a left MFG seed region (a region tightly coupled with the right MFG in controls) in the patient relative to controls. We hypothesize that this paradoxical increase in cortical coupling represents a compensatory mechanism in the patient to offset the loss of function of the resected tissue in right prefrontal cortex.

Simple exposure is sufficient to sensitize the human visual system to a particular direction of motion, but the underlying mechanisms of this process are unclear. Here, in a passive perceptual learning task, we found that exposure to task-irrelevant motion improved sensitivity to the local motion directions within the stimulus, which are processed at low levels of the visual system. In contrast, task-irrelevant motion had no effect on sensitivity to the global motion direction, which is processed at higher levels. The improvement persisted for at least several months. These results indicate that when attentional influence is limited, lower-level motion processing is more receptive to long-term modification than higher-level motion processing in the visual cortex.

Repeated experience with a visual stimulus can result in improved perception of the stimulus, i.e., perceptual learning. To understand the underlying neural mechanisms of this process, we used functional magnetic resonance imaging to track brain activations during the course of training on a contrast discrimination task. Based on their ability to improve on the task within a single scan session, subjects were separated into two groups: "learners" and "nonlearners." As learning progressed, learners showed progressively reduced activation in both visual cortex, including Brodmann's areas 18 and 19 and the fusiform gyrus, and several cortical regions associated with the attentional network, namely, the intraparietal sulcus (IPS), frontal eye field (FEF), and supplementary eye field. Among learners, the decrease in brain activations in these regions was highly correlated with the magnitude of performance improvement. Unlike learners, nonlearners showed no changes in brain activations during training. Learners showed stronger activation than nonlearners during the initial period of training in all these brain regions, indicating that one could predict from the initial activation level who would learn and who would not. In addition, over the course of training, the functional connectivity between IPS and FEF in the right hemisphere with early visual areas was stronger for learners than nonlearners. We speculate that sharpened tuning of neuronal representations may cause reduced activation in visual cortex during perceptual learning and that attention may facilitate this process through an interaction of attention-related and visual cortical regions.

Among a group of collegiate football athletes, there was a significant inverse relationship of concussion and years of football played with hippocampal volume. Years of football experience also correlated with slower reaction time. Further research is needed to determine the temporal relationships of these findings.

There has been a good deal of controversy over whether attention inf luences area V1-the first cortical area onto which information from the retina is projected. Attention to motion has been found to modulate monkey area MT and the human homolog of MT͞MST. Here we show that activation of V1 by attention to motion is task dependent. Our stimulus consisted of a group of translating random dots superimposed over another group of random dots executing expansion motion. Subjects were instructed to pay attention selectively to the translation, expansion, or neither in particular (passive condition). The activity in the human MT͞MST homolog measured by functional magnetic resonance imaging (fMRI) was significantly higher in both the translation and the expansion conditions than in the passive condition, while the activity in area V1 was significantly higher only in the translation condition. These results show that attention to motion modulates area V1, and more interestingly that highlevel cognitive processing such as attention may directly or indirectly determine the retroactive extent of feedback within the motion pathway in a manner dependent on the type of motion attended.A considerable amount of research has suggested that attention influences relatively high-level processing, but not the feature analysis level. Treisman and her colleagues built a feature integration theory in which one role of attention is to integrate visual features that are independently processed at lower level stages (1). Neurobiologically, it has been found that the responses of cells in area V4 and the inferior temporal area (IT) of macaque monkeys to an unattended stimulus are dramatically reduced (2). However, such a response reduction in cells was not found in V1, where local measurements in various features occur. On the other hand, the activity of orientation-tuned cells in V1 was found to be enhanced when subjects (macaque monkeys) attended to a specific orientation (3).With regard to the effect of attention on motion processing, at least one type of motion has been found to be driven by attention (4, 5). This finding suggests that attention is quite influential in motion processing. It has been found that attention modulates MT and MST in monkeys by means of electrophysiology (6) and the human MT͞MST homolog by functional magnetic resonance imaging (fMRI) (7).Recently, by means of both psychophysics and fMRI, it was found that when attention was directed to one of the edges of a moving wedge, the wedge appeared to move in the direction perpendicular to the attended edge-the same direction as the local component motion direction that has been suggested to be measured along that edge in V1 (8). In that case, activity in both V1 and the MT͞MST human homolog increased above non-attention levels.Then a question arises: Does attention to all types of motion activate V1? If not, what conditions activate V1? The present study has sought to answer these questions. We found that the modulation of V1 depends the type of motion to whic...