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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.
J Neurosci ; 41(31): 6714-6725, 2021 08 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.


Assuntos
Hipocampo/fisiologia , Memória Episódica , Neurônios/fisiologia , Percepção do Tempo/fisiologia , Adulto , Eletrocorticografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade
3.
Psychon Bull Rev ; 28(2): 476-486, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33205262

RESUMO

Humans can efficiently individuate a small number of objects. This subitizing ability is thought to be a consequence of limited attentional resources. However, how and what is selected during the individuation process remain outstanding questions. We investigated these in four experiments by examining if parts of objects are enumerated as efficiently as distinct objects in the presence and absence of distractor objects. We found that distractor presence reduced subitizing efficiency. Crucially, parts connected to multiple objects were enumerated less efficiently than independent objects or parts connected to a single object. These results argue against direct individuation of parts and show that objecthood plays a fundamental role in individuation. Objects are selected first and their components are selected in subsequent steps. This reveals that individuation operates sequentially over multiple levels.


Assuntos
Atenção , Julgamento , Conceitos Matemáticos , Reconhecimento Visual de Modelos , Atenção/fisiologia , Humanos , Julgamento/fisiologia , Reconhecimento Visual de Modelos/fisiologia
4.
Eur J Neurosci ; 52(12): 4639-4666, 2020 12.
Artigo em Inglês | MEDLINE | ID: mdl-32615001

RESUMO

Humans can rapidly categorise visual objects when presented in isolation. However, in everyday life we encounter multiple objects at the same time. Far less is known about how simultaneously active object representations interact. We examined such interactions by asking participants to categorise a target object at the basic (Experiment 1) or the superordinate (Experiment 2) level while the representation of another object was still active. We found that the "prime" object strongly modulated the response to the target implying that the prime's category was rapidly and automatically accessed, influencing subsequent categorical processing. Using drift diffusion modelling, we show that a prime, whose category is different from that of the target, interferes with target processing primarily during the evidence accumulation stage. This suggests that the state of category-processing neurons is altered by an active representation and this modifies the processing of other categories. Interestingly, the strength of interference increases with the similarity between the distractor and the target category. Considering these results and previous studies, we propose a general principle that category interactions are determined by the distance from a distractor's representation to the target's task-relevant categorical boundary. We argue that this principle arises from the specific architectural organisation of categories in the brain.


Assuntos
Mapeamento Encefálico , Reconhecimento Visual de Modelos , Encéfalo , Humanos , Tempo de Reação
5.
Neuroimage ; 218: 116973, 2020 09.
Artigo em Inglês | MEDLINE | ID: mdl-32464291

RESUMO

When two objects are presented in alternation at two locations, they are seen as a single object moving from one location to the other. This apparent motion (AM) percept is experienced for objects located at short and also at long distances. However, current models cannot explain how the brain integrates information over large distances to create such long-range AM. This study investigates the neural markers of AM by parcelling out the contribution of spatial and temporal interactions not specific to motion. In two experiments, participants' EEG was recorded while they viewed two stimuli inducing AM. Different combinations of these stimuli were also shown in a static context to predict an AM neural response where no motion is perceived. We compared the goodness of fit between these different predictions and found consistent results in both experiments. At short-range, the addition of the inhibitory spatial and temporal interactions not specific to motion improved the AM prediction. However, there was no indication that spatial or temporal non-linear interactions were present at long-range. This suggests that short- and long-range AM rely on different neural mechanisms. Importantly, our results also show that at both short- and long-range, responses generated by a moving stimulus could be well predicted from conditions in which no motion is perceived. That is, the EEG response to a moving stimulus is simply a combination of individual responses to non-moving stimuli. This demonstrates a dissociation between the brain response and the subjective percept of motion.


Assuntos
Encéfalo/fisiologia , Ilusões/fisiologia , Percepção de Movimento/fisiologia , Eletroencefalografia , Feminino , Humanos , Masculino , Estimulação Luminosa , Processamento de Sinais Assistido por Computador , Adulto Jovem
6.
Front Neurosci ; 12: 688, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30344471

RESUMO

The capacity of human memory is impressive. Previous reports have shown that when asked to memorize images, participants can recognize several thousands of visual objects in great details even with a single viewing of a few seconds per image. In this experiment, we tested recognition performance for natural scenes that participants saw for 20 ms only once (untrained group) or 22 times over many days (trained group) in an unrelated task. 400 images (200 previously viewed and 200 novel images) were flashed one at a time and participants were asked to lift their finger from a pad whenever they thought they had already seen the image (go/no-go paradigm). Compared to previous reports of excellent recognition performance with only single presentations of a few seconds, untrained participants were able to recognize only 64% of the 200 images they had seen few minutes before. On the other hand, trained participants, who had processed the flashed images (20 ms) several times, could correctly recognize 89% of them. EEG recordings confirmed these behavioral results. As early as 230 ms after stimulus onset, a significant event-related-potential (ERP) difference between familiar and new images was observed for the trained but not for the untrained group. These results show that briefly flashed unmasked scenes can be incidentally stored in long-term memory when repeated.

7.
Sci Rep ; 6: 38434, 2016 12 07.
Artigo em Inglês | MEDLINE | ID: mdl-27924910

RESUMO

Recent results have shown that participants can enumerate multiple parts of a single object as efficiently as multiple distinct objects, suggesting a shared mechanism for individuation of objects and object parts. Here we used the subitizing phenomenon to investigate the neural mechanism underlying the individuation of object parts. In two experiments, we measured a lateralized EEG response (N2pc) previously associated with individuation of multiple objects. In line with the subitizing effect, participants' error rate was low (less than 10%) when enumerating up to approximately three parts of an object but increased for larger numerosities. The N2pc amplitude increased as a function of the number of object parts, and reached an asymptote corresponding to the subitizing limit, replicating previous reports for separate objects. These results invite the inference that the same neural mechanism underlies individuation of multiple distinct objects and multiple parts of a single object.


Assuntos
Atenção/fisiologia , Encéfalo/fisiologia , Neurônios/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Adulto , Mapeamento Encefálico/métodos , Eletroencefalografia/métodos , Feminino , Humanos , Individuação , Masculino , Estimulação Luminosa , Tempo de Reação/fisiologia , Percepção Visual/fisiologia
8.
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
9.
Eur J Neurosci ; 39(9): 1508-16, 2014 May.
Artigo em Inglês | MEDLINE | ID: mdl-24617612

RESUMO

Basic-level categorization has long been thought to be the entry level for object representations. However, this view is now challenged. In particular, Macé et al. [M.J.-M. Macé et al. (2009) PLoS One, 4, e5927] showed that basic-level categorization (such as 'bird') requires a longer processing time than superordinate-level categorization (such as 'animal'). It has been argued that this result depends on the brief stimulus presentation times used in their study, which would degrade the visual information available. Here, we used a go/no-go paradigm to test whether the superordinate-level advantage could be observed with longer stimulus durations, and also investigated the impact of manipulating the target and distractor set heterogeneity. Our results clearly show that presentation time had no effect on categorization performance. Both target and distractor diversity influenced performance, but basic-level categories were never accessed faster or with higher accuracy than superordinate-level categories. These results argue in favor of coarse to fine visual processing to access perceptual representations.


Assuntos
Cognição , Reconhecimento Visual de Modelos , Percepção Visual , Adulto , Feminino , Humanos , Masculino , Adulto Jovem
10.
J Vis ; 12(1): 15, 2012 Jan 18.
Artigo em Inglês | MEDLINE | ID: mdl-22262913

RESUMO

Complex visual scenes can be categorized at the superordinate level (e.g., animal/non-animal or vehicle/non-vehicle) without focused attention. However, rapid visual categorization at the basic level (e.g., dog/non-dog or car/non-car) requires additional processing time. Such finer categorization might, thus, require attentional resources. This hypothesis was tested in the current study with a dual-task paradigm in which subjects performed a basic-level categorization task in peripheral vision either alone (single-task condition) or concurrently with an attentionally demanding letter discrimination task (dual-task condition). Our results indicate that basic-level categorization of either biological (dog/non-dog animal) or man-made (car/non-car vehicle) stimuli requires more information uptake but can, nevertheless, be performed when attention is not fully available, presumably because it is supported by hardwired, specialized neuronal networks.


Assuntos
Atenção/fisiologia , Discriminação Psicológica/fisiologia , Percepção de Forma/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Adulto , Condicionamento Psicológico/fisiologia , Feminino , Humanos , Masculino , Rede Nervosa/fisiologia , Estimulação Luminosa/métodos , Adulto Jovem
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