Event-related potentials reveal multiple components of proactive and reactive control in task switching

Task-switching performance relies on both proactive control processes that contribute to preparation during the cue-target interval and reactive control processes that contribute to interference control after target onset. Event-related potentials (ERPs) have excellent temporal resolution that is unmatched by other neuroimaging methods. In the context of task-switching paradigms, ERPs offer a unique approach for temporally distinguishing between proactive and reactive control processes that contribute to variability in task-switching performance. In this chapter, we highlight findings from the ERP task-switching literature that inform theoretical models of task-switching and cognitive control. Within the cue-target interval, we focus primarily on the cue-locked 'switch-positivity', a parietally-maximal increase in positivity for switch than for repeat trials. We present evidence that proactive control during task-switching involves both general and switch-specific preparation, and that switch-specific preparation itself consists of multiple processes. After target onset, we review evidence for switch-related modulation of frontocentral N2 and centroparietal P3b components that are related to conflict control and decision processes, as well as the lateralised readiness potential (LRP), which indexes processes associated with response preparation and implementation. We discuss evidence that reactive control in task-switching involves resolution of target-related interference and difficulty of task implementation processes, and that both response selection and response activation are modulated by the need to switch tasks. Finally, we present emerging evidence from studies that combine ERP measures with other techniques, such as formal cognitive modeling, functional and structural magnetic resonance imaging (MRI), and imaging genetics. We conclude that these multi-modal approaches enhance our understanding of individual differences in cognitive control and refine current neural models of cognitive control.

A critical review of brain and cognitive reserve in Huntington's disease

The ‘reserve’ hypothesis posits that the brain undergoes structural and functional reorganisation to actively cope with brain damage or disease. Consistent with passive and active components of ‘reserve’, the brain moderates its biological substrates (brain reserve) and differentially changes the level of neural activity in tasks-specific networks and/or by recruiting additional non-task related brain regions (cognitive reserve) to optimise behavioural performance. How the ‘reserve’ hypothesis applies in neurodegenerative disorders such as Huntington’s disease (HD) remains unknown. We postulate that unless the ‘reserve’ hypothesis is tested empirically, it is impossible to draw firm conclusions about how task-related neural activity is providing a neuroplastic change in HD and possibly other neurodegenerative disorders. We conclude that there is a pressing need to operationalise cognitive reserve, as well as incorporate different biological substrates into a model of ‘reserve’. We suggest that it is important to identify and embed potential neuroprotective modulating factors of ‘reserve’ in randomised controlled multi-domain non-pharmaceutical interventions to potentially enhance ‘reserve’ and thus preserve cognitive and psychosocial functioning in HD patients

Cognition uniquely maps on the metabolic and hemodynamic connectome

Data and code for results reported in manuscript "Cognition uniquely maps on the metabolic and hemodynamic connectome" (Voigt et al., submitted 2021)

Relationship between parenthood and cortical thickness in late adulthood

Pregnancy and the early postpartum period alter the structure of the brain; particularly in regions related to parental care. However, the enduring effects of this period on human brain structure and cognition in late life is unknown. Here we use magnetic resonance imaging to examine differences in cortical thickness related to parenthood in late life, for both sexes. In 235 healthy older women, we find a positive relationship between parity (number of children parented) and memory performance in mothers. Parity was also associated with differences in cortical thickness in women in the parahippocampus, precuneus, cuneus and pericalcarine sulcus. We also compared non-parents to parents of one child, in a sub-sample of older women (N = 45) and men (N = 35). For females, six regions differed in cortical thickness between parents and non-parents; these regions were consistent with those seen earlier in life in previous studies. For males, five regions differed in cortical thickness between parents and non-parents. We are first to reveal parenthood-related brain differences in late-life; our results are consistent with previously identified areas that are altered during pregnancy and the postpartum period. This study provides preliminary evidence to suggest that neural changes associated with early stages of parenthood persist into older age, and for women, may be related to marginally better cognitive outcomes

Afraid of the dark : Light acutely suppresses activity in the human amygdala

Light improves mood. The amygdala plays a critical role in regulating emotion, including fear-related responses. In rodents the amygdala receives direct light input from the retina, and light may play a role in fear-related learning. A direct effect of light on the amygdala represents a plausible mechanism of action for light’s mood-elevating effects in humans. However, the effect of light on activity in the amygdala in humans is not well understood. We examined the effect of passive dim-to-moderate white light exposure on activation of the amygdala in healthy young adults using the BOLD fMRI response (3T Siemens scanner; n = 23). Participants were exposed to alternating 30s blocks of light (10 lux or 100 lux) and dark (<1 lux), with each light intensity being presented separately. Light, compared with dark, suppressed activity in the amygdala. Moderate light exposure resulted in greater suppression of amygdala activity than dim light. Furthermore, functional connectivity between the amygdala and ventro-medial prefrontal cortex was enhanced during light relative to dark. These effects may contribute to light’s mood-elevating effects, via a reduction in negative, fear-related affect and enhanced processing of negative emotion

Incorporation of anatomical MRI knowledge for enhanced mapping of brain metabolism using functional PET

Functional positron emission tomography (fPET) imaging using continuous infusion of [18F]-fluorodeoxyglucose (FDG) is a novel neuroimaging technique to track dynamic glucose utilization in the brain. In comparison to conventional static or dynamic bolus PET, fPET maintains a sustained supply of glucose in the blood plasma which improves sensitivity to measure dynamic glucose changes in the brain, and enables mapping of dynamic brain activity in task-based and resting-state fPET studies. However, there is a trade-off between temporal resolution and spatial noise due to the low concentration of FDG and the limited sensitivity of multi-ring PET scanners. Images from fPET studies suffer from partial volume errors and residual scatter noise that may cause the cerebral metabolic functional maps to be biased. Gaussian smoothing filters used to denoise the fPET images are suboptimal, as they introduce additional partial volume errors. In this work, a post-processing framework based on a magnetic resonance (MR) Bowsher-like prior was used to improve the spatial and temporal signal to noise characteristics of the fPET images. The performance of the MR guided method was compared with conventional denosing methods using both simulated and in vivo task fPET datasets. The results demonstrate that the MR-guided fPET framework denoises the fPET images and improves the partial volume correction, consequently enhancing the sensitivity to identify brain activation, and improving the anatomical accuracy for mapping changes of brain metabolism in response to a visual stimulation task. The framework extends the use of functional PET to investigate the dynamics of brain metabolic responses for faster presentation of brain activation tasks, and for applications in low dose PET imaging

From simultaneous to synergistic MR-PET brain imaging: A review of hybrid MR-PET imaging methodologies

Simultaneous Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) scanning is a recent major development in biomedical imaging. The full integration of the PET detector ring and electronics within the MR system has been a technologically challenging design to develop but provides capacity for simultaneous imaging and the potential for new diagnostic and research capability. This article reviews state‐of‐the‐art MR‐PET hardware and software, and discusses future developments focusing on neuroimaging methodologies for MR‐PET scanning. We particularly focus on the methodologies that lead to an improved synergy between MRI and PET, including optimal data acquisition, PET attenuation and motion correction, and joint image reconstruction and processing methods based on the underlying complementary and mutual information. We further review the current and potential future applications of simultaneous MR‐PET in both systems neuroscience and clinical neuroimaging research. We demonstrate a simultaneous data acquisition protocol to highlight new applications of MR‐PET neuroimaging research studies