Matthew Hughes | Swinburne University of Technology, Hawthorn (original) (raw)

Papers by Matthew Hughes

Frontiers in Human Neuroscience, 2015

ABSTRACT Background: The stop-signal paradigm (Logan, 1984) probes the ability to inhibit on-goin... more ABSTRACT Background: The stop-signal paradigm (Logan, 1984) probes the ability to inhibit on-going responses (stopping). This involves occasional inhibition of a trained response upon presentation of a countermanding stop-signal. Stop-signal task performance can be accounted for by a race model that depicts the attempt to inhibit the go response as a race between stop-signal task processes and go task processes - the winner determines whether a response is inhibited (signal-inhibit trial) or executed (signal-respond trial). This model affords estimation of the stop-signal reaction time (SSRT) which is the finishing time of stopping processes. Neuroimaging and cortical deactivation studies have shown that right inferior frontal gyrus (IFG) is critical for stopping by demonstrating relationships between the function of right IFG and SSRT. Here we used magnetoencephalography (MEG) to explore the link between right IFG and SSRT. Methods: MEG data were recorded on an ELEKTA Neuromag TRIUX machine while a participant responded to stop-signal paradigm stimuli. Go task stimuli (Go) were left and right pointing arrows and stop-signals were auditory tones presented on 25% of trials. All trials began with a fixation cross (500ms) and stop-signal delays were varied dynamically to yield a 50% inhibition rate. The participant performed 4 blocks of stimuli (160 trials per block). After artefact rejection, trial type averages time-locked to the fixation cross were computed. Results: Mean go task RT was 361 ms and the inhibition rate was 50%. Mean stop-signal delay was 123 ms and SSRT was 238 ms. The time-frequency plot from a sensor over right IFG reveals a broad spectrum response beginning about 60 ms before SSRT on signal-inhibit trials that is not present during either signal-respond or go task trials. Conclusions: These data show that right IFG becomes active between stop-signal onset and estimated SSRT. This is the first MEG evidence indicating that right IFG is critical for stopping.

NeuroImage, 2010

We investigated ERP and fMRI correlates of anticipatory preparation and response inhibition in a ... more We investigated ERP and fMRI correlates of anticipatory preparation and response inhibition in a cued task-switching paradigm with informatively cued, non-informatively cued and no-go trials. Cue-locked ERPs showed evidence for a multicomponent preparation process. An early cue-locked differential positivity was larger for informative vs. non-informative cues and its amplitude correlated with differential activity for informatively vs. non-informatively cued trials in the dorsolateral prefrontal cortex (DLPFC), consistent with a goal activation process. A later differential positivity was larger for informatively cued switch vs. repeat trials and its amplitude correlated with informatively cued switch vs. repeat activity in the posterior parietal cortex (PPC), compatible with a category-response (C-R) rule activation process. No-go trials elicited a frontal P3, whose amplitude was negatively correlated with activity in the ventrolateral prefrontal cortex (VLPFC) and basal ganglia motor network, suggesting that a network responsible for response execution was inhibited in the course of a no-go trial. These findings indicate that anticipatory preparation in task-switching is comprised of at least two processes: goal activation and C-R rule activation. They also support a functional dissociation between DLPFC and VLPFC, with the former involved in top-down biasing and the latter involved in response inhibition.

Trials, 2013

Background: Age-related cognitive decline (ARCD) is of major societal concern in an ageing popula... more Background: Age-related cognitive decline (ARCD) is of major societal concern in an ageing population, with the development of dietary supplements providing a promising avenue for amelioration of associated deficits. Despite initial interest in the use of phospholipids (PLs) for ARCD, in recent years there has been a hiatus in such research. Because of safety concerns regarding PLs derived from bovine cortex, and the equivocal efficacy of soybean-derived PLs, there is an important need for the development of new PL alternatives. Phospholipids derived from milk proteins represent one potential candidate treatment.

Memory & Cognition, 2013

People show better memory for bizarre sentences relative to common sentences, a finding referred ... more People show better memory for bizarre sentences relative to common sentences, a finding referred to as the bizarrness effect. Interestingly, this effect is typically only obtained using a mixed-list design, in which participants study common and bizarre sentences in the same list. This bizarreness effect in mixed-list designs has been explained as the result of both enhanced encoding processes and efficient retrieval processes. The present experiment was designed to isolate the unique contributions of the retrieval context to the bizarreness effect. Participants studied common sentences in one room under one set of instructions, and bizarre sentences in another room under another set of instructions. At test, participants recalled the common and bizarre sentences either together or separately. The results showed that the bizarreness effect was only obtained when participants recalled the common and bizarre items together; no bizarreness advantage emerged when participants were required to recall the common and bizarre items separately. These results suggest that differential encoding processes are not necessary for explaining the bizarreness effect in memory. Rather, retrieval of the mixed-list context appears to be critical for obtaining the effect.

European Journal of Neuroscience, 2014

Stop-signal paradigms operationalize a basic test of goal-directed behaviour whereby an overarchi... more Stop-signal paradigms operationalize a basic test of goal-directed behaviour whereby an overarching stop goal that is performed intermittently must be maintained throughout ongoing performance of a reaction time go task (go goal). Previous studies of sustained brain activation during stop-signal task performance in humans did not observe activation of the dorsolateral prefrontal cortex (DLPFC) that, in concert with the parietal cortex, is known to subserve goal maintenance. Here we explored the hypothesis that a DLPFC and parietal network has a key role in supporting ongoing stop-signal task performance. We used a blocked functional magnetic resonance imaging design that included blocks of trials containing typical stop-signal paradigm stimuli that were performed under three conditions: Stop condition, which required reaction time responding to go stimuli and inhibition of cued responses upon presentation of a stop signal; Go condition, identical except that the tone was ignored; and Passive condition, which required only quiescent attention to stimuli. We found that, whereas a distributed corticothalamic network was more active in Stop compared with Go, only the right DLPFC and bilateral parietal cortex survived after masking that contrast with Stop compared with Passive. These findings indicate that sustained activation of a right dominant frontoparietal network supports stop goal processes during ongoing performance of the stop-signal task.

Brain Imaging and Behavior, 2008

Discovering the means to prevent and cure schizophrenia is a vision that motivates many scientist... more Discovering the means to prevent and cure schizophrenia is a vision that motivates many scientists. But in order to achieve this goal, we need to understand its neurobiological basis. The emergent metadiscipline of cognitive neuroscience fields an impressive array of tools that can be marshaled towards achieving this goal, including powerful new methods of imaging the brain (both structural and functional) as well as assessments of perceptual and cognitive capacities based on psychophysical procedures, experimental tasks and models developed by cognitive science. We believe that the integration of data from this array of tools offers the greatest possibilities and potential for advancing understanding of the neural basis of not only normal cognition but also the cognitive impairments that are fundamental to schizophrenia. Since sufficient expertise in the application of these tools and methods rarely reside in a single individual, or even a single laboratory, collaboration is a key element in this endeavor. Here, we review some of the products of our integrative efforts in collaboration with our colleagues on the East Coast of Australia and Pacific Rim. This research focuses on the neural basis of executive function deficits and impairments in early auditory processing in patients using various combinations of performance indices (from perceptual and cognitive paradigms), ERPs, fMRI and sMRI. In each case, integration of two or more sources of information provides more information than any one source alone by revealing new insights into structurefunction relationships. Furthermore, the addition of other imaging methodologies (such as DTI) and approaches (such as computational models of cognition) offers new horizons Brain Imaging and Behavior (in human brain imaging research and in understanding human behavior.

Biological Psychology, 2012

Inhibitory control deficits are well documented in schizophrenia, supported by impairment in an e... more Inhibitory control deficits are well documented in schizophrenia, supported by impairment in an established measure of response inhibition, the stop-signal reaction time (SSRT). We investigated the neural basis of this impairment by comparing schizophrenia patients and controls matched for age, sex and education on behavioural, functional magnetic resonance imaging (fMRI) and event-related potential (ERP) indices of stop-signal task performance. Compared to controls, patients exhibited slower SSRT and reduced right inferior frontal gyrus (rIFG) activation, but rIFG activation correlated with SSRT in both groups. Go stimulus and stop-signal ERP components (N1/P3) were smaller in patients, but the peak latencies of stop-signal N1 and P3 were also delayed in patients, indicating impairment early in stop-signal processing. Additionally, response-locked lateralised readiness potentials indicated response preparation was prolonged in patients. An inability to engage rIFG may predicate slowed inhibition in patients, however multiple spatiotemporal irregularities in the networks underpinning stop-signal task performance may contribute to this deficit.

Behavioural Brain Research, 2013

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European Journal of Neuroscience, 2007

Feedforward inhibition deficits have been consistently demonstrated in a range of neuropsychiatri... more Feedforward inhibition deficits have been consistently demonstrated in a range of neuropsychiatric conditions using prepulse inhibition (PPI) of the acoustic startle eye-blink reflex when assessing sensorimotor gating. While PPI can be recorded in acutely decerebrated rats, behavioural, pharmacological and psychophysiological studies suggest the involvement of a complex neural network extending from brainstem nuclei to higher order cortical areas. The current functional magnetic resonance imaging study investigated the neural network underlying PPI and its association with electromyographically (EMG) recorded PPI of the acoustic startle eye-blink reflex in 16 healthy volunteers. A sparse imaging design was employed to model signal changes in blood oxygenation level-dependent (BOLD) responses to acoustic startle probes that were preceded by a prepulse at 120 ms or 480 ms stimulus onset asynchrony or without prepulse. Sensorimotor gating was EMG confirmed for the 120-ms prepulse condition, while startle responses in the 480-ms prepulse condition did not differ from startle alone. Multiple regression analysis of BOLD contrasts identified activation in pons, thalamus, caudate nuclei, left angular gyrus and bilaterally in anterior cingulate, associated with EMGrecorded sensorimotor gating. Planned contrasts confirmed increased pons activation for startle alone vs 120-ms prepulse condition, while increased anterior superior frontal gyrus activation was confirmed for the reverse contrast. Our findings are consistent with a primary pontine circuitry of sensorimotor gating that interconnects with inferior parietal, superior temporal, frontal and prefrontal cortices via thalamus and striatum. PPI processes in the prefrontal, frontal and superior temporal cortex were functionally distinct from sensorimotor gating.