Pattern similarity in the frontoparietal control network reflects an "off-veridical" template that optimizes target-match decisions during visual search

Theories of attention hypothesize the existence of an "attentional" or "target" template that contains task-relevant information in memory when searching for an object. The target template contributes to visual search by directing visual attention towards potential targets and serving as a decisional boundary for target identification. However, debate still exists regarding how template information is stored in the human brain. Here, we conducted a pattern-based fMRI study to assess how template information is encoded to optimize target-match decisions during visual search. To ensure that match decisions reflect visual search demands, we used a visual search paradigm in which all distractors were linearly separable but highly similar to the target and were known to shift the target representation away from the distractor features (Yu & Geng, 2019). In a separate match-to-sample probe task, we measured the target representation used for match decisions across two resting state networks that have long been hypothesized to maintain and control target information: the frontoparietal control network (FPCN) and the visual network (VisN). Our results showed that lateral prefrontal cortex in FPCN maintained the context-dependent "off-veridical" template; in contrast, VisN encoded a veridical copy of the target feature during match decisions. By using behavioral drift diffusion modeling, we verified that the decision criterion during visual search and the probe task relied on a common biased target template. Taken together, our results suggest that sensory-veridical information is transformed in lateral prefrontal cortex into an adaptive code of target-relevant information that optimizes decision processes during visual search.

Potential Locations for Non-Invasive Brain Stimulation in Treating Schizophrenia: A Resting-State Functional Connectivity Analysis

Introduction: Non-invasive brain stimulation (NIBS) techniques have been widely used for the purpose of improving clinical symptoms of schizophrenia. However, the ambiguous stimulation targets may limit the efficacy of NIBS for schizophrenia. Exploring effective stimulation targets may improve the clinical efficacy of NIBS in schizophrenia.Methods: We first conducted a neurosynth-based meta-analysis of 715 functional magnetic resonance imaging studies to identify schizophrenia-related brain regions as regions of interest. Then, we performed the resting-state functional connectivity analysis in 32 patients with first-episode schizophrenia to find brain surface regions correlated with the regions of interest in three pipelines. Finally, the 10–20 system coordinates corresponding to the brain surface regions were considered as potential targets for NIBS.Results: We identified several potential targets of NIBS, including the bilateral dorsal lateral prefrontal cortex, supplementary motor area, bilateral inferior parietal lobule, temporal pole, medial prefrontal cortex, precuneus, superior and middle temporal gyrus, and superior and middle occipital gyrus. Notably, the 10-20 system location of the bilateral dorsal lateral prefrontal cortex was posterior to F3 (F4), not F3 (F4).Conclusion: Conclusively, our findings suggested that the stimulation locations corresponding to these potential targets might help clinicians optimize the application of NIBS therapy in individuals with schizophrenia.

Enhancement of task-switching performance with transcranial direct current stimulation over the right lateral prefrontal cortex

Switching between two or more tasks is a key component in our modern world. Task switching, however, requires time-consuming executive control processes and thus produces performance costs when compared to task repetitions. While executive control during task switching has been associated with activation in the lateral prefrontal cortex (lPFC), only few studies so far have investigated the causal relation between lPFC activation and task-switching performance by modulating lPFC activation. In these studies, the results of lPFC modulation were not conclusive or limited to the left lPFC. In the present study, we aimed to investigate the effect of non-invasive transcranial direct current stimulation [tDCS; anodal tDCS (1 mA, 20 min) vs. cathodal tDCS (1 mA, 20 min) vs. sham tDCS (1 mA, 30 s)] over the right inferior frontal junction on task-switching performance in a well-established task-switching paradigm. In response times, we found a significant effect of tDCS Condition (atDCS, ctDCS vs. sham) on task-switching costs, indicating the modulation of task-switching performance by tDCS. In addition, we found a task-unspecific tDCS Condition effect in the first experimental session, in which participants were least familiar with the task, indicating a general enhancement of task performance in both task repetitions and task-switching trials. Taken together, our study provides evidence that the right lPFC is involved in task switching as well as in general task processing. Further studies are needed to investigate whether these findings can be translated into clinically relevant improvement in older subjects or populations with executive function impairment.

Different neural codes serve long and short-term memory functions in primate Hippocampus and Lateral Prefrontal Cortex during virtual navigation

The primate hippocampus (HPC) and lateral prefrontal cortex (LPFC) are two brain structures deemed essential to long- and short-term memory functions respectively. Here we hypothesize that although both structures may encode similar information about the environment, the neural codes mediating neuronal communication in HPC and LPFC have differentially evolved to serve their corresponding memory functions. We used a virtual reality task in which animals navigated through a maze using a joystick and selected one of two targets in the arms of the maze according to a learned context-color rule. We found that neurons and neuronal populations in both regions encode similar information about the different task periods. Moreover, using statistical analyses and linear classifiers, we demonstrated that many HPC neurons concentrate spikes temporally into bursts, whereas most LPFC neurons sparsely distribute spikes over time. When integrating spike rates over short intervals, HPC neuronal ensembles reached maximum decoded information with fewer neurons than LPFC ensembles. We propose that HPC principal cells have evolved intrinsic properties that enable burst firing and temporal summation of synaptic potentials that ultimately facilitates synaptic plasticity and long-term memory formation. On the other hand, LPFC pyramidal cells have intrinsic properties that allow sparsely distributing spikes over time enabling encoding of short-term memories via persistent firing without necessarily triggering rapid changes in the synapses.

Life stress, sleep disturbance and depressive symptoms: The moderating role of prefrontal activation during emotion regulation

Objectives: Evidence suggests that emotion regulation difficulty may play an important role in the association between life stress, sleep disturbance and depressive symptoms. We proposed two models depicting the possible moderating roles of prefrontal cortex activation during emotion regulation in the associations among these variables and tested them. We hypothesized that (1) the association between stress and sleep disturbance would differ across prefrontal cortex activation during emotion regulation (moderation model) and (2) the indirect effects of stress on depressive symptoms through sleep disturbance would depend on prefrontal cortex activation during emotion regulation (moderated mediation model). Methods: Forty-eight healthy adults without sleep disorders based on nocturnal polysomnography participated in this study. They received functional magnetic resonance imaging scans while performing an emotion regulation task. They also completed questionnaires assessing life stress, sleep disturbance and depressive symptoms. The proposed models were tested using the PROCESS macro for SPSS. Results: As hypothesized, there was a significant moderating effect of prefrontal cortex activation during emotion regulation on the association between life stress and sleep disturbance. Furthermore, right lateral prefrontal cortex activation had a moderating role in the indirect effect of life stress on depressive symptoms through sleep disturbance. Conclusion: These findings highlight the important role of prefrontal cortex function during emotion regulation in the associations between stress, sleep disturbance and depressive symptoms. Increasing lateral prefrontal cortex recruitment when regulating the emotional response to negative life events may be critical for the prevention and intervention of depression as well as sleep problems.