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Caltech Authors (160.918 recursos)

Repository of works by Caltech published authors.

Group = Koch Laboratory

Mostrando recursos 1 - 20 de 38

  1. Inverse temporal contributions of the dorsal hippocampus and medial prefrontal cortex to the expression of long-term fear memories

    Quinn, Jennifer J.; Ma, Quang D.; Tinsley, Matthew R.; Koch, Christof; Fanselow, Michael S.
    Retrograde amnesia following disruptions of hippocampal function is often temporally graded, with recent memories being more impaired. Evidence supports the existence of one or more neocortical long-term memory storage/retrieval site(s). Neurotoxic lesions of the medial prefrontal cortex (mPFC) or the dorsal hippocampus (DH) were made 1 day or 200 days following trace fear conditioning. Recently encoded trace fear memories were most disrupted by DH lesions, while remotely encoded trace and contextual memories were most disrupted by mPFC lesions. These data strongly support the consolidation theory of hippocampus function and implicate the mPFC as a site of long-term memory storage/retrieval.

  2. Persistent Single-Neuron Activity during Working Memory in the Human Medial Temporal Lobe

    Kornblith, Simon; Quian Quiroga, Rodrigo; Koch, Christof; Fried, Itzhak; Mormann, Florian
    Working memory is an essential component of human cognition. Persistent activity related to working memory has been reported in many brain areas, including the inferior temporal and prefrontal cortex [1; 2; 3; 4; 5; 6; 7 ; 8]. The medial temporal lobe (MTL) contains “concept cells” that respond invariantly to specific individuals or places whether presented as images, text, or speech [9 ; 10]. It is unknown, however, whether the MTL also participates in working memory processes. We thus sought to determine whether human MTL neurons respond to images held in working memory. We recorded from patients with chronically intractable...

  3. Persistent Single-Neuron Activity during Working Memory in the Human Medial Temporal Lobe

    Kornblith, Simon; Quian Quiroga, Rodrigo; Koch, Christof; Fried, Itzhak; Mormann, Florian
    Working memory is an essential component of human cognition. Persistent activity related to working memory has been reported in many brain areas, including the inferior temporal and prefrontal cortex [1; 2; 3; 4; 5; 6; 7 ; 8]. The medial temporal lobe (MTL) contains “concept cells” that respond invariantly to specific individuals or places whether presented as images, text, or speech [9 ; 10]. It is unknown, however, whether the MTL also participates in working memory processes. We thus sought to determine whether human MTL neurons respond to images held in working memory. We recorded from patients with chronically intractable...

  4. Scene-selective coding by single neurons in the human parahippocampal cortex

    Mormann, Florian; Kornblith, Simon; Cerf, Moran; Ison, Matias J.; Kraskov, Alexander; Tran, Michelle; Knieling, Simeon; Quiroga, Rodrigo Quian; Koch, Christof; Fried, Itzhak
    Imaging, electrophysiological, and lesion studies have shown a relationship between the parahippocampal cortex (PHC) and the processing of spatial scenes. Our present knowledge of PHC, however, is restricted to the macroscopic properties and dynamics of bulk tissue; the behavior and selectivity of single parahippocampal neurons remains largely unknown. In this study, we analyzed responses from 630 parahippocampal neurons in 24 neurosurgical patients during visual stimulus presentation. We found a spatially clustered subpopulation of scene-selective units with an associated event-related field potential. These units form a population code that is more distributed for scenes than for other stimulus categories, and less...

  5. Effects of Chronic Sleep Restriction during Early Adolescence on the Adult Pattern of Connectivity of Mouse Secondary Motor Cortex

    Billeh, Yazan N.; Rodriguez, Alexander V.; Bellesi, Michele; Bernard, Amy; de Vivo, Luisa; Funk, Chadd M.; Harris, Julie; Honjoh, Sakiko; Mihalas, Stefan; Ng, Lydia; Koch, Christof; Cirelli, Chiara; Tononi, Giulio
    Cortical circuits mature in stages, from early synaptogenesis and synaptic pruning to late synaptic refinement, resulting in the adult anatomical connection matrix. Because the mature matrix is largely fixed, genetic or environmental factors interfering with its establishment can have irreversible effects. Sleep disruption is rarely considered among those factors, and previous studies have focused on very young animals and the acute effects of sleep deprivation on neuronal morphology and cortical plasticity. Adolescence is a sensitive time for brain remodeling, yet whether chronic sleep restriction (CSR) during adolescence has long-term effects on brain connectivity remains unclear. We used viral-mediated axonal labeling...

  6. Emergence of Slow-Switching Assemblies in Structured Neuronal Networks

    Schaub, Michael T.; Billeh, Yazan N.; Anastassiou, Costas A.; Koch, Christof; Barahona, Mauricio
    Unraveling the interplay between connectivity and spatio-temporal dynamics in neuronal networks is a key step to advance our understanding of neuronal information processing. Here we investigate how particular features of network connectivity underpin the propensity of neural networks to generate slow-switching assembly (SSA) dynamics, i.e., sustained epochs of increased firing within assemblies of neurons which transition slowly between different assemblies throughout the network. We show that the emergence of SSA activity is linked to spectral properties of the asymmetric synaptic weight matrix. In particular, the leading eigenvalues that dictate the slow dynamics exhibit a gap with respect to the bulk...

  7. Quantification and classification of neuronal responses in kernel smoothed peristimulus time histograms

    Hill, Michael R. H.; Fried, Itzhak; Koch, Christof
    Peristimulus time histograms are a widespread form of visualizing neuronal responses. Kernel convolution methods transform these histograms into a smooth, continuous probability density function. This provides an improved estimate of a neuron's actual response envelope. We here develop a classifier, called the h-coefficient, to determine whether time-locked fluctuations in the firing rate of a neuron should be classified as a response or as random noise. Unlike previous approaches, the h-coefficient takes advantage of the more precise response envelope estimation provided by the kernel convolution method. The h-coefficient quantizes the smoothed response envelope and calculates the probability of a response of...

  8. Quantification and classification of neuronal responses in kernel smoothed peristimulus time histograms

    Hill, Michael R. H.; Fried, Itzhak; Koch, Christof
    Peristimulus time histograms are a widespread form of visualizing neuronal responses. Kernel convolution methods transform these histograms into a smooth, continuous probability density function. This provides an improved estimate of a neuron's actual response envelope. We here develop a classifier, called the h-coefficient, to determine whether time-locked fluctuations in the firing rate of a neuron should be classified as a response or as random noise. Unlike previous approaches, the h-coefficient takes advantage of the more precise response envelope estimation provided by the kernel convolution method. The h-coefficient quantizes the smoothed response envelope and calculates the probability of a response of...

  9. Single-Cell Responses to Face Adaptation in the Human Medial Temporal Lobe

    Quiroga, Rodrigo Quian; Kraskov, Alexander; Mormann, Florian; Fried, Itzhak; Koch, Christof
    We used a face adaptation paradigm to bias the perception of ambiguous images of faces and study how single neurons in the human medial temporal lobe (MTL) respond to the same images eliciting different percepts. The ambiguous images were morphs between the faces of two familiar individuals, chosen because at least one MTL neuron responded selectively to one but not to the other face. We found that the firing of MTL neurons closely followed the subjects’ perceptual decisions—i.e., recognizing one person or the other. In most cases, the response to the ambiguous images was similar to the one obtained when...

  10. Single-Cell Responses to Face Adaptation in the Human Medial Temporal Lobe

    Quiroga, Rodrigo Quian; Kraskov, Alexander; Mormann, Florian; Fried, Itzhak; Koch, Christof
    We used a face adaptation paradigm to bias the perception of ambiguous images of faces and study how single neurons in the human medial temporal lobe (MTL) respond to the same images eliciting different percepts. The ambiguous images were morphs between the faces of two familiar individuals, chosen because at least one MTL neuron responded selectively to one but not to the other face. We found that the firing of MTL neurons closely followed the subjects’ perceptual decisions—i.e., recognizing one person or the other. In most cases, the response to the ambiguous images was similar to the one obtained when...

  11. Revealing cell assemblies at multiple levels of granularity

    Billeh, Yazan N.; Schaub, Michael T.; Anastassiou, Costas A.; Barahona, Mauricio; Koch, Christof
    Background: Current neuronal monitoring techniques, such as calcium imaging and multi-electrode arrays, enable recordings of spiking activity from hundreds of neurons simultaneously. Of primary importance in systems neuroscience is the identification of cell assemblies: groups of neurons that cooperate in some form within the recorded population. New method: We introduce a simple, integrated framework for the detection of cell-assemblies from spiking data without a priori assumptions about the size or number of groups present. We define a biophysically-inspired measure to extract a directed functional connectivity matrix between both excitatory and inhibitory neurons based on their spiking history. The resulting network representation is analyzed...

  12. A direct comparison of unconscious face processing under masking and interocular suppression

    Izatt, Gregory; Dubois, Julien; Faivre, Nathan; Koch, Christof
    Different combinations of forward and backward masking as well as interocular suppression have been used extensively to render stimuli invisible and to study those aspects of visual stimuli that are processed in the absence of conscious experience. Although the two techniques—masking vs. interocular suppression—obviously differ both in their applications and mechanisms, only little effort has been made to compare them systematically. Yet, such a comparison is crucial: existing discrepancies in the extent of unconscious processing inferred from these two techniques must be reconciled, as our understanding of unconscious vision should be independent of the technique used to prevent visibility. Here,...

  13. Boundary Detection Benchmarking: Beyond F-Measures

    Hou, Xiaodi; Yuille, Alan; Koch, Christof
    For an ill-posed problem like boundary detection, human labeled datasets play a critical role. Compared with the active research on finding a better boundary detector to refresh the performance record, there is surprisingly little discussion on the boundary detection benchmark itself. The goal of this paper is to identify the potential pitfalls of today's most popular boundary benchmark, BSDS 300. In the paper, we first introduce a psychophysical experiment to show that many of the "weak" boundary labels are unreliable and may contaminate the benchmark. Then we analyze the computation of f-measure and point out that the current benchmarking protocol...

  14. Simultaneous modeling of visual saliency and value computation improves predictions of economic choice

    Towal, R. Blythe; Mormann, Milica; Koch, Christof
    Many decisions we make require visually identifying and evaluating numerous alternatives quickly. These usually vary in reward, or value, and in low-level visual properties, such as saliency. Both saliency and value influence the final decision. In particular, saliency affects fixation locations and durations, which are predictive of choices. However, it is unknown how saliency propagates to the final decision. Moreover, the relative influence of saliency and value is unclear. Here we address these questions with an integrated model that combines a perceptual decision process about where and when to look with an economic decision process about what to choose. The...

  15. Category-specific visual responses of single neurons in the human medial temporal lobe

    Kreiman, Gabriel; Koch, Christof; Fried, Itzhak
    The hippocampus, amygdala and entorhinal cortex receive convergent input from temporal neocortical regions specialized for processing complex visual stimuli and are important in the representation and recognition of visual images. Recording from 427 single neurons in the human hippocampus, entorhinal cortex and amygdala, we found a remarkable degree of category-specific firing of individual neurons on a trial-by-trial basis. Of the recorded neurons, 14% responded selectively to visual stimuli from different categories, including faces, natural scenes and houses, famous people and animals. Based on the firing rate of individual neurons, stimulus category could be predicted with a mean probability of error...

  16. Imagery neurons in the human brain

    Kreiman, Gabriel; Koch, Christof; Fried, Itzhak
    Vivid visual images can be voluntarily generated in our minds in the absence of simultaneous visual input. While trying to count the number of flowers in Van Gogh's Sunflowers, understanding a description or recalling a path, subjects report forming an image in their "mind's eye". Whether this process is accomplished by the same neuronal mechanisms as visual perception has long been a matter of debate. Evidence from functional imaging, psychophysics, neurological studies and monkey electrophysiology suggests a common process, yet there are patients with deficits in one but not the other. Here we directly investigated the neuronal substrates of visual...

  17. Invariant visual representation by single neurons in the human brain

    Quian Quiroga, Rodrigo; Reddy, Leila; Kreiman, Gabriel; Koch, Christof; Fried, Itzhak
    It takes a fraction of a second to recognize a person or an object even when seen under strikingly different conditions. How such a robust, high-level representation is achieved by neurons in the human brain is still unclear. In monkeys, neurons in the upper stages of the ventral visual pathway respond to complex images such as faces and objects and show some degree of invariance to metric properties such as the stimulus size, position and viewing angle. We have previously shown that neurons in the human medial temporal lobe (MTL) fire selectively to images of faces, animals, objects or scenes....

  18. Consciousness and neurosurgery

    Crick, Francis; Koch, Christof; Kreiman, Gabriel; Fried, Itzhak
    THE NEURONAL BASIS of consciousness is the greatest challenge to the scientific world-view. Much relevant empirical work is carried out on the minimal neuronal mechanisms underlying any one specific conscious percept. Two broad approaches are popular among brain scientists: electrophysiological recordings from individual neurons in the cortex of behaving monkeys or behavior combined with functional brain imaging in humans. However, many aspects of consciousness are problematic or remain off-limits to the former approach, while the latter one lacks sufficient spatial and temporal resolution to monitor individual neurons that are key to perception, thought, memory, and action. It is here that...

  19. A Single-Neuron Correlate of Change Detection and Change Blindness in the Human Medial Temporal Lobe

    Reddy, Leila; Quian Quiroga, Rodrigo; Wilken, Patrick; Koch, Christof; Fried, Itzhak
    Observers are often unaware of changes in their visual environment when attention is not focused at the location of the change [1,2,3,4]. Because of its rather intriguing nature, this phenomenon, known as change blindness, has been extensively studied with psychophysics [5,6,7] as well as with fMRI [8,9,10,11]. However, whether change blindness can be tracked in the activity of single cells is not clear. To explore the neural correlates of change detection and change blindness, we recorded from single neurons in the human medial temporal lobe (MTL) during a change-detection paradigm. The preferred pictures of the visually responsive units elicited significantly...

  20. Sparse Representation in the Human Medial Temporal Lobe

    Waydo, Stephen; Kraskov, Alexander; Quian Quiroga, Rodrigo; Fried, Itzhak; Koch, Christof
    Recent experiments characterized individual neurons in the human medial temporal lobe with remarkably selective, invariant, and explicit responses to images of famous individuals or landmark buildings. Here, we used a probabilistic analysis to show that these data are consistent with a sparse code in which neurons respond in a selective manner to a small fraction of stimuli.

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