Anthony Singhal

The role of parietal cortex in visuomotor control : What have we learned from neuroimaging?

Research from macaque neurophysiology and human neuropsychology has implicated the parietal cortex in the sensory control of action. Functional neuroimaging has been very valuable in localizing and characterizing specific regions of the human brain involved in visuomotor actions involving different effectors, such as the eyes, head, arms and hands. Here, we review the areas discovered by human neuroimaging, including the putative functional equivalents of the following macaque regions: parietal eye fields (PEF), ventral intraparietal (VIP) area, parietal reach region (PRR) and the anterior intraparietal (AIP) area. We discuss the challenges of studying realistic movements in the imaging environment, the lateralization of visuomotor function, caveats involved in proposing interspecies homologies and the limitations and future directions for neuroimaging studies of visuomotor control.

The emotional side of cognitive distraction: Implications for road safety

Driver distraction is estimated to be one of the leading causes of motor vehicle accidents. However, little is known about the role of emotional distraction on driving, despite evidence that attention is highly biased toward emotion. In the present study, we used a dual-task paradigm to examine the potential for driver distraction from emotional information presented on roadside billboards. This purpose was achieved using a driving simulator and three different types of emotional information: neutral words, negative emotional words, and positive emotional words. Participants also responded to target words while driving and completed a surprise free recall task of all the words at the end of the study. The findings suggest that driving performance is differentially affected by the valence (negative versus positive) of the emotional content. Drivers had lower mean speeds when there were emotional words compared to neutral words, and this slowing effect lasted longer when there were positive words. This may be due to distraction effects on driving behavior, which are greater for positive arousing stimuli. Moreover, when required to process non-emotional target stimuli, drivers had faster mean speeds in conditions where the targets were interspersed with emotional words compared to neutral words, and again, these effects lasted longer when there were positive words. On the other hand, negative information led to better memory recall. These unique effects may be due to separate processes in the human attention system, particularly related to arousal mechanisms and their interaction with emotion. We conclude that distraction that is emotion-based can modulate attention and decision-making abilities and have adverse impacts on driving behavior for several reasons.

Dual-task interference is greater in delayed grasping than in visually guided grasping

Previous kinematic research suggests that visually guided grasping employs an accurate real-time control system in the dorsal stream, whereas delayed grasping relies on less accurate stored information derived by the perceptual system in the ventral stream. We explored these ideas in two experiments combining visually guided and delayed grasping with auditory tasks involving perception-based imagery and semantic memory. In both experiments, participants were cued to grasp three-dimensional objects of varying sizes. During visually guided trials, objects were visible during the interval between the cue and movement onset. During delayed trials, objects were occluded at the time of the cue. In Experiment 1, the second task required participants to listen to object names and vocally respond if the objects were of a particular shape. In Experiment 2, participants studied a paired-associates list prior to testing and then performed cued recall while grasping. The results of these experiments showed that there was reciprocal interference on both tasks, which was consistently greater during delayed grasping. Experiment 2 showed that the introduction of the second task resulted in larger grip apertures during delayed grasping. This supports the idea that delayed grasping involves processing of stored perception-based information that shares resources with cross-modal tasks involving imagery and memory.

Theta oscillations reflect a putative neural mechanism for human sensorimotor integration

Hippocampal theta oscillations (3-12 Hz) may reflect a mechanism for sensorimotor integration in rats (Bland BH. Prog Neurobiol 26: 1-54, 1986); however, it is unknown whether cortical theta activity underlies sensorimotor integration in humans. Rather, the mu rhythm (8-12 Hz) is typically found to desynchronize during movement. We measured oscillatory EEG activity for two conditions of an instructed delayed reaching paradigm. Conditions 1 and 2 were designed to differentially manipulate the contribution of the ventral visuomotor stream during the response initiation phase. We tested the hypothesis that theta activity would reflect changes in the relevant sensorimotor network: condition 2 engaged ventral stream mechanisms to a greater extent than condition 1. Theta oscillations were more prevalent during movement initiation and execution than during periods of stillness, consistent with a sensorimotor relevance for theta activity. Furthermore, theta activity was more prevalent at temporal sites in condition 2 than condition 1 during response initiation, suggesting that theta activity is present within the necessary sensorimotor network. Mu activity desynchronized more during condition 2 than condition 1, suggesting mu desynchronization is also specific to the sensorimotor network. In summary, cortical theta synchronization and mu desynchronization may represent broadly applicable rhythmic mechanisms for sensorimotor integration in the human brain.

Human fMRI Reveals That Delayed Action Re-Recruits Visual Perception

Behavioral and neuropsychological research suggests that delayed actions rely on different neural substrates than immediate actions; however, the specific brain areas implicated in the two types of actions remain unknown. We used functional magnetic resonance imaging (fMRI) to measure human brain activation during delayed grasping and reaching. Specifically, we examined activation during visual stimulation and action execution separated by a 18-s delay interval in which subjects had to remember an intended action toward the remembered object. The long delay interval enabled us to unambiguously distinguish visual, memory-related, and action responses. Most strikingly, we observed reactivation of the lateral occipital complex (LOC), a ventral-stream area implicated in visual object recognition, and early visual cortex (EVC) at the time of action. Importantly this reactivation was observed even though participants remained in complete darkness with no visual stimulation at the time of the action. Moreover, within EVC, higher activation was observed for grasping than reaching during both vision and action execution. Areas in the dorsal visual stream were activated during action execution as expected and, for some, also during vision. Several areas, including the anterior intraparietal sulcus (aIPS), dorsal premotor cortex (PMd), primary motor cortex (M1) and the supplementary motor area (SMA), showed sustained activation during the delay phase. We propose that during delayed actions, dorsal-stream areas plan and maintain coarse action goals; however, at the time of execution, motor programming requires re-recruitment of detailed visual information about the object through reactivation of (1) ventral-stream areas involved in object perception and (2) early visual areas that contain richly detailed visual representations, particularly for grasping.

Motor imagery and higher-level cognition: four hurdles before research can sprint forward

Traditionally, higher-level cognition has been described as including processes such as attention, memory, language, and decision-making. However, motor processing and motor imagery are important aspects of cognition that have typically been considered outside of the traditional view. Recent research has demonstrated that there may be a critical functional relationship between motor imagery and other higher-level cognitive processes. Here we present a review of the extant literature on motor imagery and cognition, as well as outline four hurdles that must be addressed before the field investigating the influence of motor-based processes on higher-level cognition can be moved forward. These hurdles include problems distinguishing between visual and motor processes, addressing the differences in tasks and stimuli used to evoke motor imagery, accounting for individual differences in motor imagery ability, and identifying the appropriate neural correlates. It is important that these hurdles are addressed in future research so we can sprint forward and further our knowledge about this interesting relationship.

An investigation of auditory contagious yawning

Despite a widespread familiarity with the often compelling urge to yawn after perceiving someone else yawn, an understanding of the neural mechanism underlying contagious yawning remains incomplete. In the present auditory fMRI study, listeners used a 4-point scale to indicate how much they felt like yawning following the presentation of a yawn, breath, or scrambled yawn sound. Not only were yawn sounds given significantly higher ratings, a trait positively correlated with each individual’s empathy measure, but relative to control stimuli, random effects analyses revealed enhanced hemodynamic activity in the right posterior inferior frontal gyrus (pIFG) in response to hearing yawns. Moreover, pIFG activity was greatest for yawn stimuli associated with high as opposed to low yawn ratings and for control sounds associated with equally high yawn ratings. These results support a relationship between contagious yawning and empathy and provide evidence for pIFG involvement in contagious yawning. A supplemental figure for this study may be downloaded from http://cabn.psychonomic-journals.org/content/supplemental.

Using actions to enhance memory: effects of enactment, gestures, and exercise on human memory

Few would doubt the benefits of exercise on ones physical well-being. However, the benefits of exercise on ones mental abilities are not nearly as extolled. More directly, the perspective that our bodies have a significant influence on our minds is still relatively new, though reviews by Rosenbaum (2005) and Madan and Singhal (2012a) suggest that this is beginning to change. This idea is also in line with the embodied approach to cognition (e.g., Clark, 1997; Lakoff and Johnson, 1999; Wilson, 2002; Anderson, 2003; Barsalou, 2008; Fischer and Zwaan, 2008). Briefly, embodied cognition suggests that physical properties of the human body, particularly the perceptual and motor systems, play an important role in cognition—the body influences the mind just as the mind influences the body. This approach is further supported by findings that individual body properties such as handedness can influence how individuals understand abstract concepts (Casasanto, 2009, 2011). One particularly interesting facet of the idea that our body can affect cognition is the influence of actions, gestures, and exercise on memory performance: the hypothesis is that our physical movements, and even the amount that we exercise, can affect our ability to remember. In the current paper we will provide an overview on the disparate research paradigms that support this hypothesis, and their resulting implications.

Electrophysiological correlates of fearful and sad distraction on target processing in adolescents with attention deficit-hyperactivity symptoms and affective disorders

In this study we used event-related brain potentials (ERP) as neural markers of cognitive operations to examine emotion and attentional processing in a population of high-risk adolescents with mental health problems that included attention deficit and hyperactivity disorder (ADHD), anxiety, and depression. We included a healthy control group for comparison purposes, and employed a modified version of the emotional oddball paradigm, consisting of frequent distracters (scrambled pictures), infrequent distracters (sad, fearful, and neutral pictures), and infrequent targets (circles). Participants were instructed to make a right hand button press to targets and a left hand button press to all other stimuli. EEG/ERP recordings were taken using a high-density 256-channel recording system. Behavioral data showed that for both clinical and non-clinical adolescents, reaction time (RT) was slowest in response to the fearful images. Electrophysiological data differentiated emotion and target processing between clinical and non-clinical adolescents. In the clinical group we observed a larger P100 and late positive potential (LPP) in response to fearful compared to sad or neutral pictures. There were no differences in these ERPs in the healthy sample. Emotional modulation of target processing was also identified in the clinical sample, where we observed an increase in P300 amplitude, and a larger sustained LPP in response to targets that followed emotional pictures (fear and sad) compared to targets that followed neutral pictures or other targets. There were no differences in these target ERPs for the healthy participants. Taken together, we suggest that these data provide important and novel evidence of affective and attention dysfunction in this clinical population of adolescents, and offer an example of the disruptive effects of emotional reactivity on basic cognition.

Encoding the world around us: motor-related processing influences verbal memory.

It is known that properties of words such as their imageability can influence our ability to remember those words. However, it is not known if other object-related properties can also influence our memory. In this study we asked whether a word representing a concrete object that can be functionally interacted with (i.e., high-manipulability word) would enhance the memory representations for that item compared to a word representing a less manipulable object (i.e., low-manipulability word). Here participants incidentally encoded high-manipulability (e.g., CAMERA) and low-manipulability words (e.g., TABLE) while making word judgments. Using a between-subjects design, we varied the depth-of-processing involved in the word judgment task: participants judged the words based on personal experience (deep/elaborative processing), word length (shallow), or functionality (intermediate). Participants were able to remember high-manipulability words better than low-manipulability words in both the personal experience and word length groups; thus presenting the first evidence that manipulability can influence memory. However, we observed better memory for low- than high-manipulability words in the functionality group. We explain this surprising interaction between manipulability and memory as being mediated by automatic vs. controlled motor-related cognition.