Biology subjects

Curtis, C. E.

Publications and source records attributed to Curtis, C. E..

At least 19 recordsLinked to original sources

bioRxiv2026

Neural synchrony between prefrontal and visual cortex supports visual working memory

Working memory appears to depend on neural mechanisms that are distributed across the brain. Specifically, neural activity persists in the prefrontal cortex while memories are maintained, and at the same time, the visual contents of memory can be precisely decoded from the patterns of activity in visual cortex. Contemporary models attempt to account for these findings by positing that higher-order areas, like prefrontal cortex, somehow control memory storage by recruiting encoding mechanisms in sensory cortices. Demonstrating how prefrontal cortex influences working memory representations in visual cortex is methodologically challenging and direct evidence remains scarce. Here, we leveraged the excellent temporal resolution of magnetoencephalography to test hypotheses about how synchronization of neural activity between prefrontal and visual cortex coordinates working memory representations. During a visuospatial working memory task in humans (both sexes), increased power in -band activity persisted throughout memory maintenance, and changes in its topography over visual cortex predicted both memorized locations and trialwise memory errors. Moreover, neural activity in the -band synchronized between the prefrontal and visual cortices during memory. Not only do these findings align with a large body of work demonstrating that working memories are widely distributed across the brain, but they also help explain how the prefrontal and sensory cortices communicate during memory. New & NoteworthyWhile canonical models emphasize prefrontal memory storage, recent theories propose distributed interactions between executive control and sensory areas. Using magnetoencephalography, we demonstrate that -band oscillations over visual cortex track specific memory content and synchronize with prefrontal cortex activity during maintenance. Crucially, this localized sensory activity directly predicts trial-by-trial human memory errors. These findings provide critical empirical evidence for sensory recruitment models, revealing a dynamic, oscillatory mechanism coordinating working memory.

neuroscience↗

bioRxiv2026

Visual field map size constrains working memory precision

Individual differences in working memory are associated with cognitive functioning and real-world outcomes, including general intelligence, academic achievement, and psychiatric and neurological disorders. Despite its importance, the neurobiological mechanisms that drive individual differences in working memory are unknown. Here, we asked whether the precision of spatial working memory covaries with the cortical surface area of retinotopically organized maps that are thought to store the content of working memory. In particular, we hypothesized that individuals with larger visual field maps would have more precise working memory. We assessed human subjects (male and female) working memory precision using a memory-guided saccade task, and using fMRI we separately mapped retinotopically organized regions of visual, parietal, and frontal cortex. In support of our hypothesis, we found that people with larger maps in primary visual cortex and parietal cortex had better memory. To test hypotheses about the potential mechanisms driving our results, we simulated working memory in neural network models with varying numbers of synthetic neurons. Echoing our empirical results, larger networks exhibited less memory error. This reduction in error could be fully attributed to a decrease in the proportion of memory-perturbing noise along the attractor in larger networks, establishing a pure size effect on working memory precision.

neuroscience↗

bioRxiv2025

Probabilistic working memory representations in human cortex guide behavior

Models of working memory make fundamentally different commitments to the architecture of individual memories. Information-sparse models conceptualize individual memories single point estimates agnostic to meta-cognitive variables such a uncertainty. In contrast, information-rich models propose memories re encoded s probability distributions over feature space that embed memory uncertainty in the shape of the distribution To distinguish these accounts, constructed probability distributions of memory from participants iterative reports of motion direction each trial. Remarkably, the idiosyncratic shape of these distributions (e.g., asymmetry) single trials matched the shape of neural probability distributions decoded from fMRI patterns measured from occipital and parietal cortex. Consistent with information-rich models, the neural representation of n individual memory encodes mor than the memorized feature; its variance (i.e., width and asymmetry) encodes idiosyncrasies whose read-out predicts memory behavior.

neuroscience↗

bioRxiv2025

Mnemonic maps of visual space in human prefrontal cortex

Neural theories of how the prefrontal cortex (PFC) supports working memory rely on evidence from decades of pioneering macaque research. In some respects, efforts to translate these animal models of working memory in human PFC using neuroimaging have largely failed. One possible explanation, before concluding key non-homologies between the species, is that previous neuroimaging studies used resolutions too coarse to be sensitive to intermixed distributions of neurons tuned to memorized features. To resolve this concern, we scanned human PFC at 900 micron resolution using 7T fMRI. We found that population activity in retinotopically-organized superior precentral sulcus-rather than the predicted midlateral PFC-persists during memory, encodes fine-grained information about memorized items, predicts behavioral errors in memory, and forms a stable subspace with a topological organization yoked to visual space. These results have important implications for both functional homologies between the species and theories of how the PFC supports working memory.

neuroscience↗

bioRxiv2025

Drift-like dynamics and information flow across the cortical hierarchy during working memory

Working memory is supported by widespread and distributed brain regions spanning across the cortical hierarchy. However, how working memory content evolves and is transmitted across cortical regions remains largely unknown. Here, we investigated the flow of working memory information across the cortex using time-resolved fMRI decoding. Across multiple regions in visual and parietal cortex, we found that decoded working memory content drifted over time from the memoranda towards the later errors in memory reports, consistent with drift-like dynamics predicted by attractor models. These behaviorally predictive neural memory errors emerged earliest in higher-order dorsal visual area (V3AB) and intraparietal sulcus (IPS0), and then later in early visual cortex (V1), suggesting a propagation of mnemonic information originated in higher-level visual area. Inter-areal correlation analyses revealed that during memory maintenance, information flowed predominantly in a top-down manner--from higher to lower visual areas whereas during passive viewing feedforward dynamics prevailed. Together, our findings demonstrate that working memory maintenance involves temporally structured drift dynamics and feedback-dominated information flow across cortical hierarchy, providing a mechanistic link between neural population dynamics and the formation of memory errors.

neuroscience↗

bioRxiv2025

Ketamine Alters Tuning of Neural and Behavioral Spatial Working Memory Precision

Deficits in working memory (WM) are a hallmark of neuropsy-chiatric disorders such as schizophrenia, yet their neurobiological basis remains poorly understood. Glutamate N-methyl-D-aspartate receptors (NMDARs) are critical for spatial WM (sWM), with NMDAR antagonist ketamine known to attenuate task-evoked activation and reduce sWM accuracy. Cortical microcircuit models hypothesize that NMDAR antagonism impairs sWM by broadening neural spatial tuning, but this mechanism has not been directly tested in humans. Using a pharmacological fMRI approach, we showed how ketamine broadened neural spatial tuning, attenuated activation across visual, parietal, and frontal areas, and worsened sWM performance in healthy humans. Ketamine-induced changes in tuning were more consistent across individuals and brain regions than changes in overall activation and correlated with individual differences in sWM performance. These findings provide empirical evidence linking NMDAR antagonism to disruptions in cortical microcircuit dynamics, the resulting neural tuning alterations, and sWM impairments, advancing frameworks for therapeutic development.

neuroscience↗

bioRxiv2024

Perturbing human V1 degrades the fidelity of visual working memory

Decades of macaque research established the importance of prefrontal cortex for working memory. Surprisingly, recent human neuroimaging studies demonstrated that the contents of working memory can be decoded from primary visual cortex (V1). However the necessity of this mnemonic information remains unknown and contentious. Here we provide causal evidence that transcranial magnetic stimulation targeting human V1 disrupted the fidelity of visual working memory. Errors increased only for targets remembered in the portion of the visual field disrupted by stimulation. Moreover, concurrently measured electroencephalography confirmed that stimulation disrupted not only memory behavior, but neurophysiological signatures of working memory. These results change the question from whether visual cortex is necessary for working memory to what mechanisms it uses to support memory. Moreover, they point to models in which the mechanisms supporting working memory are distributed across brain regions, including sensory areas that here we show are critical for memory storage.

neuroscience↗

bioRxiv2024

Neural mechanisms of resource allocation in working memory

To mitigate capacity limits of working memory, people allocate resources according to an items relevance. However, the neural mechanisms supporting such a critical operation remain unknown. Here, we developed computational neuroimaging methods to decode and demix neural responses associated with multiple items in working memory with different priorities. In striate and extrastriate cortex, the gain of neural responses tracked the priority of memoranda. Higher-priority memoranda were decoded with smaller error and lower uncertainty. Moreover, these neural differences predicted behavioral differences in memory prioritization. Remarkably, trialwise variability in the magnitude of delay activity in frontal cortex predicted differences in decoded precision between low and high-priority items in visual cortex. These results suggest a model in which feedback signals broadcast from frontal cortex sculpt the gain of memory representations in visual cortex according to behavioral relevance, thus, identifying a neural mechanism for resource allocation.

neuroscience↗

bioRxiv2024

Prioritizing of working memory resources depends onprefrontal cortex

How the prefrontal cortex contributes to working memory remains controversial, as theories differ in their emphasis on its role in storing memories versus controlling their content. To adjudicate between these competing ideas, we tested how perturbations to the human (both sexes) lateral prefrontal cortex impact the storage and control aspects of working memory during a task that requires human subjects to allocate resources to memory items based on their behavioral priority. Our computational model made a strong prediction that disruption of this control process would counterintuitively improve memory for low-priority items. Remarkably, transcranial magnetic stimulation of retinotopically-defined superior precentral sulcus, but not intraparietal sulcus, unbalanced the prioritization of resources, improving memory for low-priority items as predicted by the model. Therefore, these results provide direct causal support for models in which the prefrontal cortex controls the allocation of resources that support working memory, rather than simply storing the features of memoranda. SIGNIFICANCE STATEMENTAlthough higher-order cognition depends on working memory, the resources that support our memory are severely limited in capacity. To mitigate this limitation, we allocate memory resources according to the behavioral relevance of items. Nonetheless, the neural basis of these abilities remain unclear. Here, we tested the hypothesis that a region in lateral prefrontal cortex controls prioritization in working memory. Indeed, perturbing this region with transcranial magnetic stimulation disrupted the prioritization of working memory resources. Our results provide causal evidence for the hypothesis that prefrontal cortex primarily controls the allocation of memory resources, rather than storing the contents of working memory.

neuroscience↗

bioRxiv2024

Feedback scales the spatial tuning of cortical responses during visual memory

Perception, working memory, and long-term memory each evoke neural responses in visual cortex. While previous neuroimaging research on the role of visual cortex in memory has largely emphasized similarities between perception and memory, we hypothesized that responses in visual cortex would differ depending on the origins of the inputs. Using fMRI, we quantified spatial tuning in visual cortex while participants (both sexes) viewed, maintained in working memory, or retrieved from long-term memory a peripheral target. In each condition, BOLD responses were spatially tuned and aligned with the targets polar angle in all measured visual field maps including V1. As expected given the increasing sizes of receptive fields, polar angle tuning during perception increased in width up the visual hierarchy from V1 to V2, V3, hV4, and beyond. In stark contrast, the tuned responses were broad across the visual hierarchy during long-term memory (replicating a prior result) and during working memory. This pattern is consistent with the idea that mnemonic responses in V1 stem from top-down sources, even when the stimulus was recently viewed and is held in working memory. Moreover, in long-term memory, trial-to-trial biases in these tuned responses (clockwise or counterclockwise of target), predicted matched biases in memory, suggesting that the reinstated cortical responses influence memory guided behavior. We conclude that feedback widens spatial tuning in visual cortex during memory, where earlier visual maps inherit broader tuning from later maps thereby impacting the precision of memory. Significance StatementWe demonstrate that remembering a visual stimulus evokes responses in visual cortex that differ in spatial extent compared to seeing the same stimulus. Perception evokes tuned responses in early visual areas that increase in size up the visual hierarchy. Prior work showed that feedback inputs associated with long-term memory originate from later visual areas with larger receptive fields resulting in uniformly wide spatial tuning even in primary visual cortex. We replicate these results and show that the same pattern holds when maintaining in working memory a recently viewed stimulus. That trial-to-trial difficulty is reflected in the accuracy and precision of these representations suggests that visual cortex is flexibly used for processing visuospatial information, regardless of where that information originates.

neuroscience↗

bioRxiv2023

Trying harder: how cognitive effort sculpts neural representations during working memory

The neural mechanisms by which motivational factors influence cognition remain unknown. Using fMRI, we tested how cognitive effort impacts working memory (WM). Participants were precued whether WM difficulty would be hard or easy. Hard trials demanded more effort as a later decision required finer mnemonic precision. Behaviorally, pupil size was larger and response times were slower on hard trials suggesting our manipulation of effort succeeded. Neurally, we observed robust persistent activity in prefrontal cortex, especially during hard trials. We found strong decoding of location in visual cortex, where accuracy was higher on hard trials. Connecting these across-region effects, we found that the amplitude of delay period activity in frontal cortex predicted decoded accuracy in visual cortex on a trial-wise basis. We conclude that the gain of persistent activity in frontal cortex may be the source of effort-related feedback signals that improve the quality of WM representations stored in visual cortex.

neuroscience↗

bioRxiv2023

Visual working memories are abstractions of percepts

Pioneering studies demonstrating that the contents of visual working memory (WM) can be decoded from the patterns of multivoxel activity in early visual cortex transformed not only how we study WM, but theories of how memories are stored. For instance, the ability to decode the orientation of memorized gratings is hypothesized to depend on the recruitment of the same neural encoding machinery used for perceiving orientations. However, decoding evidence cannot be used to test the so-called sensory recruitment hypothesis without understanding the underlying nature of what is being decoded. Although unknown during WM, during perception decoding the orientation of gratings does not simply depend on activities of orientation tuned neurons. Rather, it depends on complex interactions between the orientation of the grating, the aperture edges, and the topographic structure of the visual map. Here, our goals are to 1) test how these aperture biases described during perception may affect WM decoding, and 2) leverage carefully manipulated visual stimulus properties of gratings to test how sensory-like are WM codes. For memoranda, we used gratings multiplied by radial and angular modulators to generate orthogonal aperture biases despite having identical orientations. Therefore, if WM representations are simply maintained sensory representations, they would have similar aperture biases. If they are abstractions of sensory features, they would be unbiased and the modulator would have no effect on orientation decoding. Results indicated that fMRI patterns of delay period activity while maintaining the orientation of a grating with one modulator (eg, radial) were interchangeable with patterns while maintaining a grating with the other modulator (eg, angular). We found significant cross-classification in visual and parietal cortex, suggesting that WM representations are insensitive to aperture biases during perception. Then, we visualized memory abstractions of stimuli using a population receptive field model of the visual field maps. Regardless of aperture biases, WM representations of both modulated gratings were recoded into a single oriented line. These results provide strong evidence that visual WM representations are abstractions of percepts, immune to perceptual aperture biases, and compel revisions of WM theory.

neuroscience↗

bioRxiv2023

Wagers for work: Decomposing the costs of cognitive effort

Some aspects of cognition are more taxing than others. Accordingly, many people will avoid cognitively demanding tasks in favor of simpler alternatives. Which components of these tasks are costly, and how much, remains unknown. Here, we use a novel task design in which subjects request wages for completing cognitive tasks and a computational modeling procedure that decomposes their wages into the costs driving them. Using working memory as a test case, our approach revealed that gating new information into memory and protecting against interference are costly. Critically, other factors, like memory load, appeared less costly. Other key factors which may drive effort costs, such as error avoidance, had minimal influence on wage requests. Our approach is sensitive to individual differences, and could be used in psychiatric populations to understand the true underlying nature of apparent cognitive deficits. Author SummaryAnyone who has tried to mentally calculate how much to tip at a restaurant knows that cognitive effort can feel aversive. Doing math in your head, like most high-level cognitive abilities, depends critically on working memory (WM). We know that WM is sometimes effortful to use, but we dont know which aspects of WM use drive these effort costs. To address this question, we had participants request wages in exchange for performing various tasks that differed in their specific WM demands. Using computational models of their wage demands, we demonstrated that some aspects of WM are costly, such as bringing new information into memory and preventing interference. Other factors, like the amount of information in memory and attempts to avoid mistakes, were less costly. Our approach identified which specific subcomponents of WM are aversive. Future research could use these methods to test theories about how motivational problems might be masquerading as cognitive deficits in psychiatric populations.

neuroscience↗

bioRxiv2022

Neural population dynamics of human working memory

Temporally evolving neural processes maintain working memory (WM) representations of information no longer available in the environment. Nonetheless, the dynamics of WM remain largely unexplored in the human cortex. With fMRI, we found evidence of both stable and dynamic WM representations in human cortex during a memory-guided saccade task. The stability of WM varied across brain regions with early visual cortex exhibiting the strongest dynamics. Leveraging population receptive field modeling, we visualized and made the neural dynamics interpretable. Early in the trial, neural responses in V1 were dominated by narrowly tuned activation at the location of the peripheral target. Over time, activity spread toward foveal locations and targets were represented by diffuse activation among voxels with receptive fields along a line between the fovea and the target. We suggest that the WM dynamics in early visual cortex reflects a transformation of sensory inputs into abstract task-related representations.

neuroscience↗

bioRxiv2021

Behavioral prioritization enhances working memory precision and neural population gain

Humans allocate visual working memory (WM) resource according to behavioral relevance, resulting in more precise memories for more important items. Theoretically, items may be maintained by feature-tuned neural populations, where the relative gain of the populations encoding each item determines precision. To test this hypothesis, we compared the amplitudes of delay-period activity in the different parts of retinotopic maps representing each of several WM items, predicting amplitude would track with behavioral priority. Using fMRI, we scanned participants while they remembered the location of multiple items over a WM delay, then reported the location of one probed item using a memory-guided saccade. Importantly, items were not equally probable to be probed (0.6, 0.3, 0.1, 0.0), which was indicated with a pre-cue. We analyzed fMRI activity in ten visual field maps in occipital, parietal, and frontal cortex known to be important for visual WM. In early visual cortex, but not association cortex, the amplitude of BOLD activation within voxels corresponding to the retinotopic location of visual WM items increased with the priority of the item. Interestingly, these results were contrasted with a common finding that higher-level brain regions had greater delay-period activity, demonstrating a dissociation between the absolute amount of activity in a brain area, and the activity of different spatially-selective populations within it. These results suggest that the distribution of WM resources according to priority sculpts the relative gains of neural populations that encode items, offering a neural mechanism for how prioritization impacts memory precision.

neuroscience↗

bioRxiv2021

Persistent Activity during Working Memory from Front to Back

Working memory (WM) extends the duration over which information is available for processing. Given its importance in supporting a wide-array of high level cognitive abilities, uncovering the neural mechanisms that underlie WM has been a primary goal of neuroscience research over the past century. Here, we critically review what we consider the two major arcs of inquiry, with a specific focus on findings that were theoretically transformative. For the first arc, we briefly review classic studies that led to the canonical WM theory that cast the prefrontal cortex (PFC) as a central player utilizing persistent activity of neurons as a mechanism for memory storage. We then consider recent challenges to the theory regarding the role of persistent neural activity. The second arc, which evolved over the last decade, stemmed from sophisticated computational neuroimaging approaches enabling researchers to decode the contents of WM from the patterns of neural activity in many parts of the brain including early visual cortex. We summarize key findings from these studies, their implications for WM theory, and finally the challenges these findings pose. A comprehensive theory of WM will require a unification of these two arcs of research.

neuroscience↗

bioRxiv2021

Joint representation of working memory and uncertainty in human cortex

Neural representations of visual working memory (VWM) are noisy, and thus, decisions based on VWM are inevitably subject to uncertainty. However, the mechanisms by which the brain simultaneously represents the content and uncertainty of memory remain largely unknown. Here, inspired by the theory of probabilistic population codes, we test the hypothesis that the human brain represents an item maintained in VWM as a probability distribution over stimulus feature space, thereby capturing both its content and uncertainty. We used a neural generative model to decode probability distributions over memorized locations from fMRI activation patterns. We found that the mean of the probability distribution decoded from retinotopic cortical areas predicted memory reports on a trial-by-trial basis. Moreover, in several of the same mid-dorsal stream areas the spread of the distribution predicted subjective trial-by-trial uncertainty judgments. These results provide evidence that VWM content and uncertainty are jointly represented by probabilistic neural codes.

neuroscience↗

bioRxiv2021

Working Memory Representations in Visual Cortex Mediate the Effects of Distraction

Although the contents of working memory (WM) can be decoded from activity in visual cortex, these representations may play a limited role if they are not robust to distraction. Here, we used model-based fMRI to estimate the impact that a distracting visual task had on WM representations in several visual field maps in visual and frontoparietal association cortex. Distraction caused the fidelity of WM representations in all maps to briefly dip when both the memorandum and distractor were jointly encoded by the population activities. Moreover, distraction induced small biases in memory errors which were predicted by biases in neural decoding in early visual cortex, but not other regions. Although distraction briefly disrupts WM representations, the widespread redundancy with which WM information is encoded may protect against catastrophic loss. In early visual cortex, nonetheless, the neural representation of information in WM and behavioral performance were intertwined, solidifying its importance in memory.

neuroscience↗