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1.
Nat Commun ; 12(1): 4839, 2021 08 10.
Artigo em Inglês | MEDLINE | ID: mdl-34376673

RESUMO

The ability to maintain a sequence of items in memory is a fundamental cognitive function. In the rodent hippocampus, the representation of sequentially organized spatial locations is reflected by the phase of action potentials relative to the theta oscillation (phase precession). We investigated whether the timing of neuronal activity relative to the theta brain oscillation also reflects sequence order in the medial temporal lobe of humans. We used a task in which human participants learned a fixed sequence of pictures and recorded single neuron and local field potential activity with implanted electrodes. We report that spikes for three consecutive items in the sequence (the preferred stimulus for each cell, as well as the stimuli immediately preceding and following it) were phase-locked at distinct phases of the theta oscillation. Consistent with phase precession, spikes were fired at progressively earlier phases as the sequence advanced. These findings generalize previous findings in the rodent hippocampus to the human temporal lobe and suggest that encoding stimulus information at distinct oscillatory phases may play a role in maintaining sequential order in memory.


Assuntos
Potenciais de Ação/fisiologia , Epilepsia/fisiopatologia , Aprendizagem/fisiologia , Neurônios/fisiologia , Ritmo Teta/fisiologia , Adolescente , Adulto , Epilepsia/diagnóstico , Feminino , Hipocampo/citologia , Hipocampo/fisiologia , Humanos , Masculino , Modelos Neurológicos , Neurônios/citologia , Estimulação Luminosa/métodos , Lobo Temporal/citologia , Lobo Temporal/fisiologia , Adulto Jovem
2.
Nat Commun ; 12(1): 4029, 2021 06 29.
Artigo em Inglês | MEDLINE | ID: mdl-34188047

RESUMO

The representation of space in mouse visual cortex was thought to be relatively uniform. Here we reveal, using population receptive-field (pRF) mapping techniques, that mouse visual cortex contains a region in which pRFs are considerably smaller. This region, the "focea," represents a location in space in front of, and slightly above, the mouse. Using two-photon imaging we show that the smaller pRFs are due to lower scatter of receptive-fields at the focea and an over-representation of binocular regions of space. We show that receptive-fields of single-neurons in areas LM and AL are smaller at the focea and that mice have improved visual resolution in this region of space. Furthermore, freely moving mice make compensatory eye-movements to hold this region in front of them. Our results indicate that mice have spatial biases in their visual processing, a finding that has important implications for the use of the mouse model of vision.


Assuntos
Movimentos Oculares/fisiologia , Córtex Visual/fisiologia , Campos Visuais/fisiologia , Percepção Visual/fisiologia , Animais , Feminino , Movimentos da Cabeça/fisiologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Estimulação Luminosa
3.
J Neurosci ; 41(31): 6714-6725, 2021 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-34183446

RESUMO

An indispensable feature of episodic memory is our ability to temporally piece together different elements of an experience into a coherent memory. Hippocampal time cells-neurons that represent temporal information-may play a critical role in this process. Although these cells have been repeatedly found in rodents, it is still unclear to what extent similar temporal selectivity exists in the human hippocampus. Here, we show that temporal context modulates the firing activity of human hippocampal neurons during structured temporal experiences. We recorded neuronal activity in the human brain while patients of either sex learned predictable sequences of pictures. We report that human time cells fire at successive moments in this task. Furthermore, time cells also signaled inherently changing temporal contexts during empty 10 s gap periods between trials while participants waited for the task to resume. Finally, population activity allowed for decoding temporal epoch identity, both during sequence learning and during the gap periods. These findings suggest that human hippocampal neurons could play an essential role in temporally organizing distinct moments of an experience in episodic memory.SIGNIFICANCE STATEMENT Episodic memory refers to our ability to remember the what, where, and when of a past experience. Representing time is an important component of this form of memory. Here, we show that neurons in the human hippocampus represent temporal information. This temporal signature was observed both when participants were actively engaged in a memory task, as well as during 10-s-long gaps when they were asked to wait before performing the task. Furthermore, the activity of the population of hippocampal cells allowed for decoding one temporal epoch from another. These results suggest a robust representation of time in the human hippocampus.

4.
Curr Biol ; 29(24): 4268-4275.e7, 2019 12 16.
Artigo em Inglês | MEDLINE | ID: mdl-31786063

RESUMO

Neuronal response to sensory stimuli depends on the context. The response in primary visual cortex (V1), for instance, is reduced when a stimulus is surrounded by a similar stimulus [1-3]. The source of this surround suppression is partially known. In mouse, local horizontal integration by somatostatin-expressing interneurons contributes to surround suppression [4]. In primates, however, surround suppression arises too quickly to come from local horizontal integration alone, and myelinated axons from higher visual areas, where cells have larger receptive fields, are thought to provide additional surround suppression [5, 6]. Silencing higher visual areas indeed decreased surround suppression in the awake primate by increasing responses to large stimuli [7, 8], although not under anesthesia [9, 10]. In smaller mammals, like mice, fast surround suppression could be possible without feedback. Recent studies revealed a small reduction in V1 responses when silencing higher areas [11, 12] but have not investigated surround suppression. To determine whether higher visual areas contribute to V1 surround suppression, even when this is not necessary for fast processing, we inhibited the areas lateral to V1, particularly the lateromedial area (LM), a possible homolog of primate V2 [13], while recording in V1 of awake and anesthetized mice. We found that part of the surround suppression depends on activity from lateral visual areas in the awake, but not anesthetized, mouse. Inhibiting the lateral visual areas specifically increased responses in V1 to large stimuli. We present a model explaining how excitatory feedback to V1 can have these suppressive effects for large stimuli.


Assuntos
Inibição Neural/fisiologia , Córtex Visual/metabolismo , Vigília/fisiologia , Animais , Masculino , Camundongos , Camundongos Transgênicos , Neurônios/fisiologia , Orientação/fisiologia , Estimulação Luminosa/métodos , Córtex Visual/fisiologia , Campos Visuais , Vias Visuais/fisiologia , Percepção Visual/fisiologia
5.
Curr Biol ; 29(12): R574-R577, 2019 06 17.
Artigo em Inglês | MEDLINE | ID: mdl-31211977

RESUMO

The lateral geniculate nucleus of the thalamus (LGN) is a relay nucleus between the retina and the visual cortex. A new brain imaging study shows that LGN activity is modulated by figure-ground organization, even when the figure and ground are presented to different eyes: a hallmark of a cortical feedback effect.


Assuntos
Corpos Geniculados , Córtex Visual , Atenção , Humanos , Retina , Tálamo
6.
Curr Biol ; 29(6): 1019-1029.e4, 2019 03 18.
Artigo em Inglês | MEDLINE | ID: mdl-30853432

RESUMO

During visual perception, the brain enhances the representations of image regions that belong to figures and suppresses those that belong to the background. Natural images contain many regions that initially appear to be part of a figure when analyzed locally (proto-objects) but are actually part of the background if the whole image is considered. These proto-grounds must be correctly assigned to the background to allow correct shape identification and guide behavior. To understand how the brain resolves this conflict between local and global processing, we recorded neuronal activity from the primary visual cortex (V1) of macaque monkeys while they discriminated between n/u shapes that have a central proto-ground region. We studied the fine-grained spatiotemporal profile of neural activity evoked by the n/u shape and found that neural representation of the object proceeded from a coarse-to-fine resolution. Approximately 100 ms after the stimulus onset, the representation of the proto-ground region was enhanced together with the rest of the n/u surface, but after ∼115 ms, the proto-ground was suppressed back to the level of the background. Suppression of the proto-ground was only present in animals that had been trained to perform the shape-discrimination task, and it predicted the choice of the animal on a trial-by-trial basis. Attention enhanced figure-ground modulation, but it had no effect on the strength of proto-ground suppression. The results indicate that the accuracy of scene segmentation is sharpened by a suppressive process that resolves local ambiguities by assigning proto-grounds to the background.


Assuntos
Macaca mulatta/fisiologia , Neurônios/fisiologia , Reconhecimento Visual de Modelos , Córtex Visual/fisiologia , Animais , Masculino , Estimulação Luminosa
7.
Neuroimage ; 197: 806-817, 2019 08 15.
Artigo em Inglês | MEDLINE | ID: mdl-28648888

RESUMO

High resolution laminar fMRI is beginning to probe responses in the different layers of cortex. What can we expect this exciting new technique to discover about cortical processing and how can we verify that it is producing an accurate picture of the underlying laminar differences in neural processing? This review will address our knowledge of laminar cortical circuitry gained from electrophysiological studies in macaque monkeys with a focus on the primary visual cortex, as this area has been most often targeted in both laminar electrophysiological and fMRI studies. We will review how recent studies are attempting to verify the accuracy of laminar fMRI by recreating the known laminar profiles of various neural tuning properties. Furthermore, we will examine how feedforward and feedback-related neural processes engage different cortical layers, producing canonical patterns of spiking and synaptic activity as estimated by the analysis of current-source density. These results provide a benchmark for recent studies aiming to examine the profiles of bottom-up and top-down processes with laminar fMRI. Finally, we will highlight particularly useful paradigms and approaches which may help us to understand processing in the different layers of the human cerebral cortex.


Assuntos
Benchmarking , Córtex Cerebral/fisiologia , Imageamento por Ressonância Magnética/métodos , Neurônios/fisiologia , Animais , Mapeamento Encefálico/métodos , Mapeamento Encefálico/normas , Humanos , Imageamento por Ressonância Magnética/normas
8.
Sci Rep ; 8(1): 17800, 2018 12 12.
Artigo em Inglês | MEDLINE | ID: mdl-30542060

RESUMO

Figure-ground segregation is the process by which the visual system identifies image elements of figures and segregates them from the background. Previous studies examined figure-ground segregation in the visual cortex of monkeys where figures elicit stronger neuronal responses than backgrounds. It was demonstrated in anesthetized mice that neurons in the primary visual cortex (V1) of mice are sensitive to orientation contrast, but it is unknown whether mice can perceptually segregate figures from a background. Here, we examined figure-ground perception of mice and found that mice can detect figures defined by an orientation that differs from the background while the figure size, position or phase varied. Electrophysiological recordings in V1 of awake mice revealed that the responses elicited by figures were stronger than those elicited by the background and even stronger at the edge between figure and background. A figural response could even be evoked in the absence of a stimulus in the V1 receptive field. Current-source-density analysis suggested that the extra activity was caused by synaptic inputs into layer 2/3. We conclude that the neuronal mechanisms of figure-ground segregation in mice are similar to those in primates, enabling investigation with the powerful techniques for circuit analysis now available in mice.


Assuntos
Neurônios/fisiologia , Córtex Visual/fisiologia , Percepção Visual/fisiologia , Vigília/fisiologia , Animais , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Orientação/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Estimulação Luminosa/métodos
9.
Sci Rep ; 7(1): 9036, 2017 08 22.
Artigo em Inglês | MEDLINE | ID: mdl-28831043

RESUMO

We can learn new tasks by listening to a teacher, but we can also learn by trial-and-error. Here, we investigate the factors that determine how participants learn new stimulus-response mappings by trial-and-error. Does learning in human observers comply with reinforcement learning theories, which describe how subjects learn from rewards and punishments? If yes, what is the influence of selective attention in the learning process? We developed a novel redundant-relevant learning paradigm to examine the conjoint influence of attention and reward feedback. We found that subjects only learned stimulus-response mappings for attended shapes, even when unattended shapes were equally informative. Reward magnitude also influenced learning, an effect that was stronger for attended than for non-attended shapes and that carried over to a subsequent visual search task. Our results provide insights into how attention and reward jointly determine how we learn. They support the powerful learning rules that capitalize on the conjoint influence of these two factors on neuronal plasticity.


Assuntos
Atenção , Aprendizagem , Recompensa , Adulto , Feminino , Humanos , Masculino , Estimulação Luminosa , Tempo de Reação , Reforço Psicológico , Reprodutibilidade dos Testes , Adulto Jovem
10.
Sci Rep ; 7(1): 7585, 2017 08 08.
Artigo em Inglês | MEDLINE | ID: mdl-28790394

RESUMO

Faces are important visual objects for humans and other social animals. A complex network of specialized brain areas is involved in the recognition and interpretation of faces. This network needs to strike a balance between being sensitive enough to distinguish between different faces with similar features, and being tolerant of low-level visual changes so that a given face is stably perceived as a particular individual. Such stability may require feedback from higher brain regions down to the level where details are represented. Here, we describe a phenomenon in which interocular competition between face features is stabilized and eliminated when observers attend high-level face characteristics. Two different face images presented to the individual eyes do not cause the perceptual fluctuations that are typically observed in binocular rivalry. Instead, they merge into a stable percept of an intermediate face that combines features from both eyes' images. The stability of the intermediate face percept depends on the observer attending holistic face properties such as identity or gender. It disappears when observers explicitly attend facial features, suggesting a crucial role of top-down stabilizing feedback from high-level areas that represent holistic faces back to lower processing levels where detailed face features compete for conscious representation.


Assuntos
Reconhecimento Facial , Percepção Visual , Adulto , Feminino , Humanos , Masculino , Estimulação Luminosa , Visão Binocular , Adulto Jovem
12.
Curr Biol ; 27(7): R269-R271, 2017 04 03.
Artigo em Inglês | MEDLINE | ID: mdl-28376334

RESUMO

How does the brain hold information about multiple stimuli online after they have disappeared? A new study shows that neurons in the human medial temporal remain active while images are memorized, demonstrating that spiking activity keeps multiple memories online.


Assuntos
Memória de Curto Prazo , Neurociências , Encéfalo , Humanos , Neurônios , Lobo Temporal
13.
Neuron ; 93(1): 9-11, 2017 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-28056347

RESUMO

In this issue of Neuron, Nandy et al. (2017) reveal a number of important new insights into the neural mechanisms that are responsible for attentional selection.


Assuntos
Atenção , Neurônios , Humanos
14.
Nat Commun ; 8: 13804, 2017 01 05.
Artigo em Inglês | MEDLINE | ID: mdl-28054544

RESUMO

Neuronal activity in early visual cortex depends on attention shifts but the contribution to working memory has remained unclear. Here, we examine neuronal activity in the different layers of the primary visual cortex (V1) in an attention-demanding and a working memory task. A current-source density analysis reveales top-down inputs in the superficial layers and layer 5, and an increase in neuronal firing rates most pronounced in the superficial and deep layers and weaker in input layer 4. This increased activity is strongest in the attention task but it is also highly reliable during working memory delays. A visual mask erases the V1 memory activity, but it reappeares at a later point in time. These results provide new insights in the laminar circuits involved in the top-down modulation of activity in early visual cortex in the presence and absence of visual stimuli.


Assuntos
Atenção , Memória de Curto Prazo , Neurônios/fisiologia , Córtex Visual/fisiologia , Potenciais de Ação , Animais , Mapeamento Encefálico , Eletrodos , Fixação Ocular , Macaca mulatta , Masculino , Estimulação Luminosa , Movimentos Sacádicos , Córtex Visual/citologia , Córtex Visual/fisiopatologia
15.
Cereb Cortex ; 26(10): 3964-76, 2016 10.
Artigo em Inglês | MEDLINE | ID: mdl-27522074

RESUMO

Segregation of images into figures and background is fundamental for visual perception. Cortical neurons respond more strongly to figural image elements than to background elements, but the mechanisms of figure-ground modulation (FGM) are only partially understood. It is unclear whether FGM in early and mid-level visual cortex is caused by an enhanced response to the figure, a suppressed response to the background, or both.We studied neuronal activity in areas V1 and V4 in monkeys performing a texture segregation task. We compared texture-defined figures with homogeneous textures and found an early enhancement of the figure representation, and a later suppression of the background. Across neurons, the strength of figure enhancement was independent of the strength of background suppression.We also examined activity in the different V1 layers. Both figure enhancement and ground suppression were strongest in superficial and deep layers and weaker in layer 4. The current-source density profiles suggested that figure enhancement was caused by stronger synaptic inputs in feedback-recipient layers 1, 2, and 5 and ground suppression by weaker inputs in these layers, suggesting an important role for feedback connections from higher level areas. These results provide new insights into the mechanisms for figure-ground organization.


Assuntos
Neurônios/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Córtex Visual/fisiologia , Potenciais de Ação , Animais , Atenção/fisiologia , Eletrodos Implantados , Medições dos Movimentos Oculares , Haplorrinos , Testes Neuropsicológicos , Estimulação Luminosa , Processamento de Sinais Assistido por Computador
16.
Elife ; 52016 06 13.
Artigo em Inglês | MEDLINE | ID: mdl-27291188

RESUMO

After an initial stage of local analysis within the retina and early visual pathways, the human visual system creates a structured representation of the visual scene by co-selecting image elements that are part of behaviorally relevant objects. The mechanisms underlying this perceptual organization process are only partially understood. We here investigate the time-course of perceptual grouping of two-dimensional image-regions by measuring the reaction times of human participants and report that it is associated with the gradual spread of object-based attention. Attention spreads fastest over large and homogeneous areas and is slowed down at locations that require small-scale processing. We find that the time-course of the object-based selection process is well explained by a 'growth-cone' model, which selects surface elements in an incremental, scale-dependent manner. We discuss how the visual cortical hierarchy can implement this scale-dependent spread of object-based attention, leveraging the different receptive field sizes in distinct cortical areas.


Assuntos
Atenção , Encéfalo/fisiologia , Percepção Visual , Humanos , Tempo de Reação , Córtex Visual/fisiologia , Vias Visuais/fisiologia
17.
PLoS Biol ; 14(3): e1002420, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-27015604

RESUMO

Here we report the first quantitative analysis of spiking activity in human early visual cortex. We recorded multi-unit activity from two electrodes in area V2/V3 of a human patient implanted with depth electrodes as part of her treatment for epilepsy. We observed well-localized multi-unit receptive fields with tunings for contrast, orientation, spatial frequency, and size, similar to those reported in the macaque. We also observed pronounced gamma oscillations in the local-field potential that could be used to estimate the underlying spiking response properties. Spiking responses were modulated by visual context and attention. We observed orientation-tuned surround suppression: responses were suppressed by image regions with a uniform orientation and enhanced by orientation contrast. Additionally, responses were enhanced on regions that perceptually segregated from the background, indicating that neurons in the human visual cortex are sensitive to figure-ground structure. Spiking responses were also modulated by object-based attention. When the patient mentally traced a curve through the neurons' receptive fields, the accompanying shift of attention enhanced neuronal activity. These results demonstrate that the tuning properties of cells in the human early visual cortex are similar to those in the macaque and that responses can be modulated by both contextual factors and behavioral relevance. Our results, therefore, imply that the macaque visual system is an excellent model for the human visual cortex.


Assuntos
Córtex Visual/fisiologia , Percepção Visual/fisiologia , Potenciais de Ação , Adulto , Animais , Atenção/fisiologia , Feminino , Humanos , Macaca , Imageamento por Ressonância Magnética
18.
Nat Commun ; 6: 8556, 2015 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-26449885

RESUMO

Neuronal processes underlying the formation of new associations in the human brain are not yet well understood. Here human participants, implanted with depth electrodes in the brain, learned arbitrary associations between images presented in an ordered, predictable sequence. During learning we recorded from medial temporal lobe (MTL) neurons that responded to at least one of the pictures in the sequence (the preferred stimulus). We report that as a result of learning, single MTL neurons show asymmetric shifts in activity and start firing earlier in the sequence in anticipation of their preferred stimulus. These effects appear relatively early in learning, after only 11 exposures to the stimulus sequence. The anticipatory neuronal responses emerge while the subjects became faster in reporting the next item in the sequence. These results demonstrate flexible representations that could support learning of new associations between stimuli in a sequence, in single neurons in the human MTL.


Assuntos
Epilepsia/fisiopatologia , Aprendizagem , Neurônios/fisiologia , Lobo Temporal/fisiopatologia , Adolescente , Adulto , Eletroencefalografia , Epilepsia/psicologia , Feminino , Humanos , Masculino , Neurônios/química , Lobo Temporal/química , Lobo Temporal/citologia , Adulto Jovem
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