16 research outputs found
An fMRI investigation of moral cognition in healthcare decision making
This study used fMRI to investigate the neural substrates of moral cognition in
health resource allocation decision problems. In particular, it investigated the
cognitive and emotional processes that underpin utilitarian approaches to health
care rationing such as Quality Adjusted Life Years (QALYs). Participants viewed
hypothetical medical and nonmedical resource allocation scenarios which described
equal or unequal allocation of resources to different groups. In addition, participants
were assigned to 1 of 2 treatments in which they either did or did not receive
advanced instructions about the principles of utilitarianism. In all cases, participants
were asked to judged the proposed allocations as âfairâ or âunfair.â More
brain activity was observed within the superior parietal lobe, angular gyrus, middle
temporal gyrus, and bilateral caudate nucleus when participants viewed scenarios
depicting equal divisions of resources. Conversely, unequal resource divisions were
associated with more activity in the inferior frontal gyrus and insula cortex.
Furthermore, instructions about the principles of utilitarianism led to significant
activation differences within the inferior frontal gyrus and the middle frontal gyrus.
Significant differences in activity were also found within the inferior frontal cortex
and anterior insula between medical and nonmedical scenarios. The implications
for cognitive control mechanisms and the cognitive and neural bases of utilitarian
ethical judgment are discussed
The role of the lateral prefrontal cortex and anterior cingulate in stimulusâresponse association reversals
Many complex tasks require us to flexibly switch between
behavioral rules, associations, and strategies. The prefrontal cerebral cortex is thought to be critical to the performance of such behaviors, although the relative contribution of different components of this structure and associated subcortical regions are not fully understood. We used functional magnetic resonance imaging to measure brain activity during a simple task which required repeated reversals of a rule linking a colored cue and a left/right motor response. Each trial comprised three discrete events separated by variable delay periods. A colored cue instructed which response was to be executed, followed by a go signal which told the subject to execute the response and a feedback instruction which indicated whether to ââholdââ or ââf lipââ the rule linking the colored cue and response. The design allowed us to determine which brain regions were recruited by the specific demands of
preparing a rule contingent motor response, executing such a
response, evaluating the significance of the feedback, and
reconfiguring stimulusâresponse (SR) associations. The results indicate that an increase in neural activity occurs within the anterior cingulate gyrus under conditions in which SR associations are labile. In contrast, lateral frontal regions are activated by unlikely/unexpected perceptual events regardless of their significance for behavior. A network of subcortical structures, including the mediodorsal nucleus of the thalamus and striatum were the only regions showing activity that was exclusively correlated with the neurocognitive demands of reversing SR associations. We conclude that lateral frontal regions act to evaluate the behavioral significance of perceptual
events, whereas medial frontalâthalamic circuits are involved in monitoring and reconfiguring SR associations when necessary
Bilateral redundancy gain and callosal integrity in a man with callosal lipoma: a diffusion-tensor imaging study
We investigated whether abnormalities in the structural organisation of the corpus callosum in the presence of curvilinear lipoma are associated with increased facilitation of response time to bilateral stimuli, an effect known as the redundancy gain. A patient (A.J.) with a curvilinear lipoma of the corpus callosum, his genetically-identical twin, and age-matched control participants made speeded responses to luminant stimuli. Structural organisation of callosal regions was assessed with diffusion-tensor imaging. A.J. was found to have reduced structural integrity in the splenium of the corpus callosum and produced a large redundancy gain suggestive of neural summation
The role of the dominant versus the non-dominant hemisphere: an fMRI study of Aphasia recovery following stroke
Background: Speech production is one of the most frequently affected cognitive functions following stroke; however, the neural mechanisms underlying the recovery of speech function are still incompletely understood.
Aims: The current study aims to address the differential contributions of the dominant and non-dominant hemispheres in recovery from aphasia following stroke by comparing data from four stroke patients and 12 control participants to assess the patterns of activation during speech production tasks during functional magnetic resonance imaging (fMRI) scanning.
Methods & Procedures: Four chronic stroke patients (three left-hemisphere lesion and one right-hemisphere lesion) diagnosed with Brocaâs aphasia at the acute phase, but now recovered to near normal speech ability, were tested on speech production tasks (phonemic fluency, categorical fluency and picture naming) whilst undergoing fMRI. These patients were compared with 12 healthy controls undergoing the same procedure.
Outcomes & Results: Individual subject analysis showed activation peaks in perilesional areas in three out of four patients. This included one patient with right-hemisphere lesion, who also showed predominant perilesional activation. Group analysis of control participants showed predominately left-hemisphere activation, but not exclusively so. Laterality indexes were calculated and showed predominant left-hemisphere lateralisation in the control group (LI = 0.4). Three out of the four patients showed speech lateralised to the same hemisphere as their lesion and the fourth patient showed speech lateralised to the opposite hemisphere to their lesion. Different speech production tasks resulted in varying lateralisation indices (LIs) within participants.
Conclusions: The data suggest that perilesional areas support recovery of speech in the chronic phase post-stroke regardless of the site of the lesion. The study has implications for the understanding of functional recovery as well as for the paradigms used in fMRI to localise speech production areas. Specifically, a variety of speech tasks are required to elicit activation that is representative of the range of cortical involvement in speech in healthy adults and that also allows for accurate reporting of the extent of recovery experienced in patients
Bilateral redundancy gain and callosal integrity in a man with callosal lipoma: a diffusion-tensor imaging study
We investigated whether abnormalities in the structural organisation of the corpus callosum in the presence of curvilinear lipoma are associated with increased facilitation of response time to bilateral stimuli, an effect known as the redundancy gain. A patient (A.J.) with a curvilinear lipoma of the corpus callosum, his genetically-identical twin, and age-matched control participants made speeded responses to luminant stimuli. Structural organisation of callosal regions was assessed with diffusion-tensor imaging. A.J. was found to have reduced structural integrity in the splenium of the corpus callosum and produced a large redundancy gain suggestive of neural summation
The neural correlates of working memory training in typically developing children.
Working memory training improves children's cognitive performance on untrained tasks; however, little is known about the underlying neural mechanisms. This was investigated in 32 typically developing children aged 10-14Â years (19Â girls and 13 boys) using a randomized controlled design and multi-modal magnetic resonance imaging (Devon, UK; 2015-2016). Training improved working memory performance and increased intrinsic functional connectivity between the bilateral intraparietal sulci. Furthermore, improvements in working memory were associated with greater recruitment of the left middle frontal gyrus on a complex span task. Repeated engagement of fronto-parietal regions during training may increase their activity and functional connectivity over time, affording greater working memory performance. The plausibility of generalizable cognitive benefits from a neurobiological perspective and implications for neurodevelopmental theory are discussed
Value-based decision-making of cigarette and nondrug rewards in dependent and occasional cigarette smokers:An FMRI study
Little is known about the neural functioning that underpins drug valuation and choice in addiction, including nicotine dependence. Following ad libitum smoking, 19 dependent smokers (smokedâ„10/day) and 19 occasional smokers (smoked 0.5â5/week) completed a decisionâmaking task. First, participants stated how much they were willingâtoâpay for various amounts of cigarettes and shop vouchers. Second, during functional magnetic resonance imaging, participants decided if they wanted to buy these cigarettes and vouchers for a set amount of money. We examined decisionâmaking behaviour and brain activity when faced with cigarette and voucher decisions, purchasing (vs not purchasing) cigarettes and vouchers, and âvalue signalsâ where brain activity correlated with cigarette and voucher value. Dependent smokers had a higher willingnessâtoâpay for cigarettes and greater activity in the bilateral middle temporal gyrus when faced with cigarette decisions than occasional smokers. Across both groups, the decision to buy cigarettes was associated with activity in the left paracingulate gyrus, right nucleus accumbens, and left amygdala. The decision to buy vouchers was associated with activity in the left superior frontal gyrus, but dependent smokers showed weaker activity in the left posterior cingulate gyrus than occasional smokers. Across both groups, cigarette value signals were observed in the left striatum and ventromedial prefrontal cortex. To summarise, nicotine dependence was associated with greater behavioural valuation of cigarettes and brain activity during cigarette decisions. When purchasing cigarettes and vouchers, reward and decisionârelated brain regions were activated in both groups. For the first time, we identified value signals for cigarettes in the brain
Lomustine nanoparticles enable both bone marrow sparing and high brain drug levels - a strategy for brain cancer treatments
Detection of experimental ERP effects in combined EEG-fMRI: evaluating the benefits of interleaved acquisition and Independent Component Analysis
Copyright © 2011 Elsevier. NOTICE: this is the authorâs version of a work that was accepted for publication in Clinical Neurophysiology . Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Clinical Neurophysiology, 2011 Vol. 122 Issue 2, pp. 267-77 DOI: http://dx.doi.org/10.1016/j.clinph.2010.06.033Objective
The present study examined the benefit of rapid alternation of EEG and fMRI (a common strategy for avoiding artifact caused by rapid switching of MRI gradients) for detecting experimental modulations of ERPs in combined EEGâfMRI. The study also assessed the advantages of aiding the extraction of specific ERP components by means of signal decomposition using Independent Component Analysis (ICA).
Methods
âGoânogoâ task stimuli were presented either during fMRI scanning or in the gaps between fMRI scans, resulting in âgradientâ and âno-gradientâ ERPs. âGoânogoâ differences in the N2 and P3 components were subjected to conventional ERP analysis, as well as single-trial and reliability analyses.
Results
Comparable N2 and P3 enhancement on ânogoâ trials was found in the âgradientâ and âno-gradientâ ERPs. ICA-based signal decomposition resulted in better validity (as indicated by topography), greater stability and lower measurement error of the predicted ERP effects.
Conclusions
While there was little or no benefit of acquiring ERPs in the gaps between fMRI scans, ICA decomposition did improve the detection of experimental ERP modulations.
Significance
Simultaneous and continuous EEGâfMRI acquisition is preferable to interleaved protocols. ICA-based decomposition is useful not only for artifact cancellation, but also for the extraction of specific ERP components
Multi-modal representation of effector modality in frontal cortex during rule switching.
We report a functional magnetic resonance imaging (fMRI) study which investigated whether brain areas involved in updating task rules within the frontal lobe of the cerebral cortex show activity related to the modality of motor response used in the task. Participants performed a rule switching task using different effector modalities. In some blocks participants responded with left/right button presses, whilst in other blocks left/right saccades were required. The color of a Cue event instructed a left or right response based upon a rule, followed by a Feedback which indicated whether the rule was to stay the same or "Flip" on the next trial. The findings revealed variation in the locus of activity within the ventrolateral frontal cortex dependent upon effector modality. Other frontal areas showed no significant difference in activity between response epochs but changed their pattern of connectivity with posterior cortical areas dependent upon response. Multivariate analysis revealed that the pattern of activity evoked by Flip rule Feedbacks within an apparently supra modal frontal region (dorsolateral frontal cortex) discriminated between response epochs. The results are consistent with the existence of multi-modal representations of stimulus-response (SR) rules within the frontal cerebral cortex