Biomedical subjects

Gregory McCarthy

Publications and source records attributed to Gregory McCarthy.

At least 19 recordsLinked to original sources

PubMed2007

Guided saccades modulate object and face-specific activity in the fusiform gyrus.

We investigated the influence of saccadic eye movements on the magnitude of functional MRI (fMRI) activation in brain regions known to participate in object and face perception. In separate runs, subjects viewed a static image of a uniform gray field, a face, or a flower. Every 500 ms a small fixation cross made a discrete jump within the image and subjects were required to make a saccade and fixate the cross at its new location. Each run consisted of alternating blocks in which the subject was guided to make small and large saccades. A comparison of large vs. small saccade blocks revealed robust activity in the oculomotor system, particularly within the frontal eye fields (FEF), intraparietal sulcus (IPS), and superior colliculi regardless of the background image. Activity within portions of the ventral occipitotemporal cortex (VOTC) including the lingual and fusiform gyri was also modulated by saccades, but here saccade-related activity was strongly influenced by the background image. Activity within the VOTC was strongest when large saccadic eye movements were made over an image of a face or a flower compared to a uniform gray image. Of most interest was activity in the functionally predefined face-specific region of the fusiform gyrus, where large saccades made over a face increased activity, but where similar large saccades made over a flower or a uniform gray field did not increase activity. These results demonstrate the potentially confounding influence of uncontrolled eye movements for neuroimaging studies of face and object perception.

Adult↗

PubMed2006

fMRI reveals that involuntary visual deviance processing is resource limited.

Previous studies suggest that involuntary auditory attention evoked by unattended auditory stimuli is not influenced by the primary focus of attention. However, prior studies from our laboratory have found that processing of unattended auditory deviant tones in the auditory and frontal regions is modulated by top-down attentional demands and resource availability. Whether processing of unattended visual deviant stimuli is altered by the availability of attentional resources has not been established. The goal of the current study was to examine the automaticity of these activations, their modulation by attentional capacity, and the neuroanatomical distribution of any attentional effects upon visual deviance detection. We designed an event-related functional magnetic resonance imaging (fMRI) study during which subjects performed a continuous perceptual-motor-visual tracking task whose difficulty was modulated by changing the control dynamics of a joystick. Changes in the anatomical localization, spatial distribution, and intensity of the blood oxygenation level-dependent (BOLD) response associated with unattended infrequent visual changes were examined during low- and high-difficulty tracking conditions of the primary visual task. Results revealed that the unattended deviants elicited BOLD activation in the visual, fusiform, and parietal regions. In these regions, the intensity and extent of the activation evoked by the deviants decreased as a function of the demands of the primary visual task. These findings suggest that processing of unattended visual deviant stimuli is restricted by the attentional demands of a primary task, as previously demonstrated for unattended auditory deviant tones.

Adolescent↗

PubMed2006

Role of the inferior frontal cortex in coping with distracting emotions.

The role of inferior frontal cortex in coping with emotional distracters presented concurrently with a working memory task was investigated using event-related functional magnetic resonance imaging. The study yielded two main findings: (i) processing of emotional distracters was associated with enhanced functional coupling between the amygdala and the inferior frontal cortex and (ii) the inferior frontal cortex showed a left-lateralized activation pattern discriminating successful from unsuccessful trials in the presence of emotional distraction. These findings provide evidence that coping with emotional distraction entails interactions between brain regions responsible for detection and inhibition of emotional distraction, and identified a hemispheric specialization in the inferior frontal cortex in controlling the impact of distracting emotions on cognitive performance (left hemisphere) vs. controlling the subjective feeling of being distracted (right hemisphere).

Adaptation, Psychological↗

PubMed2006

Mood alters amygdala activation to sad distractors during an attentional task.

BACKGROUND: A behavioral hallmark of mood disorders is biased perception and memory for sad events. The amygdala is poised to mediate internal mood and external event processing because of its connections with both the internal milieu and the sensory world. There is little evidence showing that the amygdala's response to sad sensory stimuli is functionally modulated by mood state, however. METHODS: We investigated the impact of mood on amygdala activation evoked by sad and neutral pictures presented as distractors during an attentional oddball task. Healthy adults underwent functional magnetic resonance imaging during task runs that were preceded by sad or happy movie clips. Happy and sad mood induction was conducted within-subjects on consecutive days in counterbalanced order. RESULTS: Amygdala activation to sad distractors was enhanced after viewing sad movies relative to happy ones and was correlated with reaction time costs to detect attentional targets. The activation was higher in female subjects in the right hemisphere. The anterior cingulate, ventromedial and orbital prefrontal cortex, insula, and other posterior regions also showed enhanced responses to sad distractors during sad mood. CONCLUSIONS: These findings reveal brain mechanisms that integrate emotional input and current mood state, with implications for understanding cognitive distractibility in depression.

Adult↗

PubMed2006

Occipitotemporal activation evoked by the perception of human bodies is modulated by the presence or absence of the face.

We investigated the degree to which activation in regions of the brain known to participate in social perception is influenced by the presence or absence of the face and other body parts. Subjects continuously viewed a static image of a lecture hall in which actors appeared briefly in various poses. There were three conditions: Body-Face, in which the actor appeared with limbs, torso, and face clearly visible; Body-Only, in which the actor appeared with his or her face occluded by a book; and Face-Only, in which the actor appeared behind a podium with only face and shoulders visible. Using event-related functional MRI, we obtained strong activation in those regions previously identified as important for face and body perception. These included portions of the fusiform (FFG) and lingual gyri within ventral occipitotemporal cortex (VOTC), and portions of the middle occipital gyrus (corresponding to the previously defined extrastriate body area, or EBA) and posterior superior temporal sulcus (pSTS) within lateral occipitotemporal cortex (LOTC). Activation of the EBA was strongest for the Body-Only condition; indeed, exposing the face decreased EBA activation evoked by the body. In marked contrast, activation in the pSTS was largest when the face was visible, regardless of whether the body was also visible. Activity within the lateral lingual gyrus and adjacent medial FFG was strongest for the Body-Only condition, while activation in the lateral FFG was greatest when both the face and body were visible. These results provide new information regarding the importance of a visible face in both the relative activation and deactivation of brain structures engaged in social perception.

Adult↗

PubMed2006

Brain systems mediating cognitive interference by emotional distraction.

Flexible behavior depends on our ability to cope with distracting stimuli that can interfere with the attainment of goals. Emotional distracters can be particularly disruptive to goal-oriented behavior, but the neural systems through which these detrimental effects are mediated are not known. We used event-related functional magnetic resonance imaging to investigate the effect of emotional and nonemotional distracters on a delayed-response working memory (WM) task. As expected, this task evoked robust activity during the delay period in typical WM regions (dorsolateral prefrontal cortex and lateral parietal cortex). Presentation of emotional distracters during the delay interval evoked strong activity in typical emotional processing regions (amygdala and ventrolateral prefrontal cortex) while simultaneously evoking relative deactivation of the WM regions and impairing WM performance. These results provide the first direct evidence that the detrimental effect of emotional distracters on ongoing cognitive processes entails the interaction between a dorsal neural system associated with "cold" executive processing and a ventral system associated with "hot" emotional processing.

Adolescent↗

PubMed2005

Visual task complexity modulates the brain's response to unattended auditory novelty.

New, unusual, and changing events are important environmental cues, and the ability to detect these types of stimuli in the environment constitutes a biologically significant survival skill. We used event-related potentials to examine whether sensory and cognitive neural responses to unattended novel events are modulated by the complexity of a primary visuomotor task. Event-related potentials were elicited by unattended task-irrelevant pitch-deviant tones and novel environmental sounds while study participants performed a continuous visuomotor tracking task at two levels of difficulty, achieved by manipulating the control dynamics of a joystick. The results revealed that increased task complexity modulated evoked sensory and cognitive event-related potential components, indicating that detection of change and novelty in the unattended auditory channel is resource-limited.

Acoustic Stimulation↗

PubMed2005

Taking an "intentional stance" on eye-gaze shifts: a functional neuroimaging study of social perception in children.

During middle childhood, children develop an increasing understanding of intentions and other social information conveyed through dynamic facial cues such as changes in eye-gaze direction. Recent work in our laboratory has focused on using functional magnetic resonance imaging (fMRI) in adults to map the neural circuitry subserving the visual analysis of others' actions and the intentions underlying these actions. In these studies, the superior temporal sulcus (STS) region has been continually implicated in processing shifts in eye gaze. Further, these studies have indicated that STS activity is modulated by the context within which eye-gaze shifts occur, suggesting that this region is involved in social perception via its role in the analysis of the intentions of observed actions. Still, no studies have investigated the neural circuitry supporting eye-gaze processing in children. We used event-related fMRI to examine brain activity in 7- to 10-year-old healthy children observing an animated virtual actor who shifted her eyes towards either a target object or empty space. Consistent with prior studies in adults, the STS, middle temporal gyrus, and inferior parietal lobule were sensitive to the intentions underlying the stimulus character's eye movements. These findings suggest that the neural circuitry underlying the processing of eye gaze and the detection of intentions conveyed through shifts in eye gaze in children are similar to that found previously in adults. We discuss these findings and potential implications for mapping the neurodevelopment of the social cognition and social perception abnormalities characteristic of autism.

Aging↗

PubMed2005

Decisions under uncertainty: probabilistic context influences activation of prefrontal and parietal cortices.

Many decisions are made under uncertainty; that is, with limited information about their potential consequences. Previous neuroimaging studies of decision making have implicated regions of the medial frontal lobe in processes related to the resolution of uncertainty. However, a different set of regions in dorsal prefrontal and posterior parietal cortices has been reported to be critical for selection of actions to unexpected or unpredicted stimuli within a sequence. In the current study, we induced uncertainty using a novel task that required subjects to base their decisions on a binary sequence of eight stimuli so that uncertainty changed dynamically over time (from 20 to 50%), depending on which stimuli were presented. Activation within prefrontal, parietal, and insular cortices increased with increasing uncertainty. In contrast, within medial frontal regions, as well as motor and visual cortices, activation did not increase with increasing uncertainty. We conclude that the brain response to uncertainty depends on the demands of the experimental task. When uncertainty depends on learned associations between stimuli and responses, as in previous studies, it modulates activation in the medial frontal lobes. However, when uncertainty develops over short time scales as information is accumulated toward a decision, dorsal prefrontal and posterior parietal contributions are critical for its resolution. The distinction between neural mechanisms subserving different forms of uncertainty resolution provides an important constraint for neuroeconomic models of decision making.

Adult↗

PubMed2005

Neural basis of eye gaze processing deficits in autism.

Impairments in using eye gaze to establish joint attention and to comprehend the mental states and intentions of other people are striking features of autism. Here, using event-related functional MRI (fMRI), we show that in autism, brain regions involved in gaze processing, including the superior temporal sulcus (STS) region, are not sensitive to intentions conveyed by observed gaze shifts. On congruent trials, subjects watched as a virtual actor looked towards a checkerboard that appeared in her visual field, confirming the subject's expectation regarding what the actor 'ought to do' in this context. On incongruent trials, she looked towards empty space, violating the subject's expectation. Consistent with a prior report from our laboratory that used this task in neurologically normal subjects, 'errors' (incongruent trials) evoked more activity in the STS and other brain regions linked to social cognition, indicating a strong effect of intention in typically developing subjects (n = 9). The same brain regions were activated during observation of gaze shifts in subjects with autism (n = 10), but did not differentiate congruent and incongruent trials, indicating that activity in these regions was not modulated by the context of the perceived gaze shift. These results demonstrate a difference in the response of brain regions underlying eye gaze processing in autism. We conclude that lack of modulation of the STS region by gaze shifts that convey different intentions contributes to the eye gaze processing deficits associated with autism.

Adolescent↗

PubMed2005

Functional anatomy of biological motion perception in posterior temporal cortex: an FMRI study of eye, mouth and hand movements.

Passive viewing of biological motion engages extensive regions of the posterior temporal-occipital cortex in humans, particularly within and nearby the superior temporal sulcus (STS). Relatively little is known about the functional specificity of this area. Some recent studies have emphasized the perceived intentionality of the motion as a potential organizing principle, while others have suggested the existence of a somatotopy based upon the limb perceived in motion. Here we conducted an event-related functional magnetic resonance imaging experiment to compare activity elicited by movement of the eyes, mouth or hand. Each motion evoked robust activation in the right posterior temporal-occipital cortex. While there was substantial overlap of the activation maps in this region, the spatial distribution of hemodynamic response amplitudes differentiated the movements. Mouth movements elicited activity along the mid-posterior STS while eye movements elicited activity in more superior and posterior portions of the right posterior STS region. Hand movements activated more inferior and posterior portions of the STS region within the posterior continuing branch of the STS. Hand-evoked activity also extended into the inferior temporal, middle occipital and lingual gyri. This topography may, in part, reflect the role of particular body motions in different functional activities.

Adult↗

PubMed2005

Amygdala activation to sad pictures during high-field (4 tesla) functional magnetic resonance imaging.

Fear-related processing in the amygdala has been well documented, but its role in signaling other emotions remains controversial. The authors recovered signal loss in the amygdala at high-field strength using an inward spiral pulse sequence and probed its response to pictures varying in their degree of portrayed sadness. These pictures were presented as intermittent task-irrelevant distractors during a concurrent visual oddball task. Relative to neutral distractors, sad distractors elicited greater activation along ventral brain regions, including the amygdala, fusiform gyrus, and inferior frontal gyrus. In contrast, oddball targets engaged dorsal sectors of frontal, parietal, and cingulate cortices. The amygdala's role in emotional evaluation thus extends to images of grief and despair as well as to those depicting violence and threat.

Adult↗

PubMed2005

Regional brain activation evoked when approaching a virtual human on a virtual walk.

We investigated the necessity of biological motion for activation of the posterior superior temporal sulcus (pSTS) in circumstances in which the rapid approach of the observer to a virtual human induced the observer to make inferences about the characters intentions. Using a virtual reality environment, subjects experienced themselves walking towards a complex scene composed of animate and/or inanimate objects. During "person" trials, the scene contained a virtual human either making a simple gesture such as scratching his face (Study 1) or standing completely still (Study 2). During "object" trials, the scenes contained items such as furniture, a face portrait, and a clock, but not the virtual human. Using functional MRI to measure brain activity, we demonstrated strong activity in the pSTS while the observer approached the social scene, but only when the virtual human was making gestures. This result emphasizes the importance of biological motion in inferring the intentions of others.

Adolescent↗

PubMed2005

Graded visual attention modulates brain responses evoked by task-irrelevant auditory pitch changes.

Previous studies suggested that auditory change-specific neural responses are attention-independent and reflect central auditory processing. The automaticity of the brain's response to infrequent changes in pitch within a series of auditory tone pips was examined in parallel functional magnetic resonance imaging (fMRI) and event-related potential (ERP) studies. Subjects performed a continuous perceptual-motor visual tracking task at two levels of difficulty while simultaneously hearing a series of task-irrelevant standard tone pips and infrequent pitch-deviant tones. fMRI results revealed that the unattended pitch-deviant tones strongly activated superior temporal and frontal cortical regions. These activations were significantly modulated by the tracking difficulty of the primary task. ERP results revealed that the amplitude of the scalp-negative component evoked by deviant tones (MMN) was attenuated during the more difficult tracking task. Our results demonstrate that the brain's response to task-irrelevant sensory changes is strongly influenced by intermodal attentional demands.

Acoustic Stimulation↗

PubMed2004

Dynamic and strategic aspects of executive processing.

Executive cognitive functions have been postulated to include both dynamic behavioral selection and strategic goal-setting or response preparation. To investigate the relation between these aspects of executive processing, we embedded an event-related oddball paradigm within a blocked design. Subjects responded to infrequent targets presented within a series of standard stimuli that required no response; this task alternated with a visually similar nontask condition. Using functional magnetic resonance imaging (fMRI), we found that a set of brain regions including dorsolateral prefrontal cortex (dlPFC), insular cortex, cingular cortex, and the basal ganglia demonstrated transient activation both to target stimuli and to the onset of task blocks. Within the parietal cortex, there was a dissociation such that the supramarginal gyrus exhibited greater activity to the target stimuli than to block onsets, while the converse pattern was observed in the intraparietal sulcus. Sustained positive activity during task blocks was present in the caudate and supplementary motor area, while sustained negative activity was present in the precuneus and medial parietal cortex. We conclude that dlPFC and related brain regions mediate both dynamic and strategic processing, through the preparation and selection of rules for behavior.

Adolescent↗

PubMed2004

Emotion-attention network interactions during a visual oddball task.

Emotional and attentional functions are known to be distributed along ventral and dorsal networks in the brain, respectively. However, the interactions between these systems remain to be specified. The present study used event-related functional magnetic resonance imaging (fMRI) to investigate how attentional focus can modulate the neural activity elicited by scenes that vary in emotional content. In a visual oddball task, aversive and neutral scenes were presented intermittently among circles and squares. The squares were frequent standard events, whereas the other novel stimulus categories occurred rarely. One experimental group [N=10] was instructed to count the circles, whereas another group [N=12] counted the emotional scenes. A main effect of emotion was found in the amygdala (AMG) and ventral frontotemporal cortices. In these regions, activation was significantly greater for emotional than neutral stimuli but was invariant to attentional focus. A main effect of attentional focus was found in dorsal frontoparietal cortices, whose activity signaled task-relevant target events irrespective of emotional content. The only brain region that was sensitive to both emotion and attentional focus was the anterior cingulate gyrus (ACG). When circles were task-relevant, the ACG responded equally to circle targets and distracting emotional scenes. The ACG response to emotional scenes increased when they were task-relevant, and the response to circles concomitantly decreased. These findings support and extend prominent network theories of emotion-attention interactions that highlight the integrative role played by the anterior cingulate.

Adult↗

PubMed2004

What is odd in the oddball task? Prefrontal cortex is activated by dynamic changes in response strategy.

In the "oddball" target detection task, subjects respond to target stimuli that occur infrequently and irregularly within a series of standard stimuli. Although detection of these targets reliably evokes transient activity in prefrontal cortical regions, it has not been established whether this activity is due to selection of an infrequent response or to changes in response strategy. We investigated this issue using a novel variant of the oddball task that incorporated the Simon effect, while measuring hemodynamic brain activity in prefrontal cortex using functional magnetic resonance imaging (fMRI). Subjects viewed a series of circles and squares that required left and right button presses, respectively. On 90% of trials ("standard" trials), the stimuli were presented in the same visual hemifield as the hand of response, but on 10% of trials ("strategy-change" trials) they were presented in the opposite visual hemifield. Significant activation to the infrequent strategy-change trials was found in the anterior middle frontal gyrus (MFG), the posterior inferior frontal gyrus (IFG) and adjacent insular cortex, and in the anterior cingulate gyrus (ACG). These regions, which correspond to previous reports of oddball-related activation, were consistent across subjects. Behavioral results supported our interpretation that subjects potentiated a position-based response strategy, which was inhibited on the strategy-change trials. Activity within the MFG and ACG was much greater on error trials than on correct trials, while IFG activity was similar between error and correct trials. We conclude that the dorsolateral prefrontal cortex (dlPFC) is associated with dynamic changes in the mapping of stimuli to responses (e.g. response strategies), independently of any changes in behavior.

Adolescent↗

PubMed2004

Linking hemodynamic and electrophysiological measures of brain activity: evidence from functional MRI and intracranial field potentials.

We investigated the relation between electrophysiological and hemodynamic measures of brain activity through comparison of intracranially recorded event-related local field potentials (ERPs) and blood-oxygenation level dependent functional magnetic resonance imaging (BOLD fMRI). We manipulated the duration of visual checkerboard stimuli across trials and measured stimulus-duration-related changes in ERP and BOLD activity in three brain regions: peri-calcarine cortex, the fusiform gyrus and lateral temporal-occipital (LTO) cortex. ERPs were recorded from patients who had indwelling subdural electrodes as part of presurgical testing, while BOLD responses were measured in similar brain regions in a second set of subjects. Similar BOLD responses were measured in peri-calcarine and fusiform regions, with both showing monotonic but non-linear increases in hemodynamic amplitude with stimulus duration. In sharp contrast, very different ERP responses were observed in these same regions, such that calcarine electrodes exhibited onset potentials, sustained activity over the course of stimulus duration and prominent offset potentials, while fusiform electrodes only exhibited onset potentials that did not vary with stimulus duration. No duration-related ERP or BOLD changes were observed in LTO. Additional analyses revealed no consistent changes in the EEG spectrum across different brain sites that correlated with duration-related changes in the BOLD response. We conclude that the relation between ERPs and fMRI differs across brain regions.

Adult↗