Papers by Bernard Romeo Gomes
Nature Neuroscience
While experience unfolds continuously, memories are organized as a set of discrete events that bi... more While experience unfolds continuously, memories are organized as a set of discrete events that bind together the "where", "when", and "what" of episodic memory. This segmentation of continuous experience is thought to be facilitated by the detection of salient environmental or cognitive events. However, the underlying neural mechanisms and how such segmentation shapes episodic memory representations remain unclear. We recorded from single neurons in the human medial temporal lobe while subjects watched videos with different types of embedded boundaries and were subsequently evaluated for memories of the video contents. Here we show neurons that signal the presence of cognitive boundaries between subevents from the same episode and neurons that detect the abstract separation between different episodes. The firing rate and spike timing of these boundary-responsive neurons were predictive of later memory retrieval accuracy. At the population level, abrupt neural state changes following boundaries predicted enhanced memory strength but impaired order memory, capturing the behavioral tradeoff subjects exhibited when recalling episodic content versus temporal order. Successful retrieval was associated with reinstatement of the neural state present following boundaries, indicating that boundaries structure memory search. These findings reveal a neuronal substrate for detecting cognitive boundaries and show that cognitive boundary signals facilitate the mnemonic organization of continuous experience as a set of discrete episodic events.
Working memory (WM) is an essential component of executive functions which depend on maintaining ... more Working memory (WM) is an essential component of executive functions which depend on maintaining task-related information online for brief periods in both the presence and absence of interfering stimuli. Active maintenance occurs during the WM delay period, the time between stimulus encoding and subsequent retrieval. Previous studies have extensively documented prefrontal (PFC) and posterior parietal (PPC) cortex activity during the WM delay period, but the role of subcortical structures including the thalamus remains to be fully elucidated, especially in humans. Using simultaneous EEG-fMRI, we investigated the role of the thalamus during the WM delay period following low and high memory load encoding. During the delay, participants passively viewed scrambled images containing similar color and spatial frequency to serve as a perceptual baseline. Using individual fMRI-weighted source analyses centered around delay period onset, the effects of increased and decreased memory load on m...
Frontiers in Psychology, 2022
Spontaneous eye blink rate (sEBR) has been linked to attention and memory, specifically working m... more Spontaneous eye blink rate (sEBR) has been linked to attention and memory, specifically working memory (WM). sEBR is also related to striatal dopamine (DA) activity with schizophrenia and Parkinson’s disease showing increases and decreases, respectively, in sEBR. A weakness of past studies of sEBR and WM is that correlations have been reported using blink rates taken at baseline either before or after performance of the tasks used to assess WM. The goal of the present study was to understand how fluctuations in sEBR during different phases of a visual WM task predict task accuracy. In two experiments, with recordings of sEBR collected inside and outside of a magnetic resonance imaging bore, we observed sEBR to be positively correlated with WM task accuracy during the WM delay period. We also found task-related modulation of sEBR, including higher sEBR during the delay period compared to rest, and lower sEBR during task phases (e.g., stimulus encoding) that place demands on visual at...
A critical manipulation used to study the neural basis of working memory (WM) is to vary the info... more A critical manipulation used to study the neural basis of working memory (WM) is to vary the information load at encoding followed by measurements of activity and connectivity during maintenance in the subsequent delay period. The hallmark finding is that delay period activity and connectivity increases between frontal and parietal brain regions as load is increased. Most WM studies, however, employ simple stimuli (e.g., simple shapes or letters) during encoding and utilize unfilled intervals (e.g., a blank screen or fixation cross) during the delays. In the present study, we asked how delay period activity and connectivity change during low and high load maintenance of complex stimuli. Twenty-two participants completed a modified Sternberg WM task with two or five naturalistic scenes as stimuli while scalp EEG was recorded. In each trial, the delay interval was filled with phase scrambled scenes to provide a visual perceptual control with color and spatial frequency similar to the ...
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Papers by Bernard Romeo Gomes