Synchronization and assembly formation in the visual cortex.
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Animals↗
Biomedical subjects
A K Kreiter
Publications and source records attributed to A K Kreiter.
Testing non-linearity and directedness of interactions between neural groups in the macaque inferotemporal cortex.
Information processing in the visual cortex depends on complex and context sensitive patterns of interactions between neuronal groups in many different cortical areas. Methods used to date for disentangling this functional connectivity presuppose either linearity or instantaneous interactions, assumptions that are not necessarily valid. In this paper a general framework that encompasses both linear and non-linear modelling of neurophysiological time series data by means of Local Linear Non-linear Autoregressive models (LLNAR) is described. Within this framework a new test for non-linearity of time series and for non-linearity of directedness of neural interactions based on LLNAR is presented. These tests assess the relative goodness of fit of linear versus non-linear models via the bootstrap technique. Additionally, a generalised definition of Granger causality is presented based on LLNAR that is valid for both linear and non-linear systems. Finally, the use of LLNAR for measuring non-linearity and directional influences is illustrated using artificial data, reference data as well as local field potentials (LFPs) from macaque area TE. LFP data is well described by the linear variant of LLNAR. Models of this sort, including lagged values of the preceding 25 to 60 ms, revealed the existence of both uni- and bi-directional influences between recording sites.
Action Potentials↗
Neural codes: firing rates and beyond.
Computational neuroscience has contributed significantly to our understanding of higher brain function by combining experimental neurobiology, psychophysics, modeling, and mathematical analysis. This article reviews recent advances in a key area: neural coding and information processing. It is shown that synapses are capable of supporting computations based on highly structured temporal codes. Such codes could provide a substrate for unambiguous representations of complex stimuli and be used to solve difficult cognitive tasks, such as the binding problem. Unsupervised learning rules could generate the circuitry required for precise temporal codes. Together, these results indicate that neural systems perform a rich repertoire of computations based on action potential timing.
Action Potentials↗
Stimulus-dependent synchronization of neuronal responses in the visual cortex of the awake macaque monkey.
In visual areas of the cerebral cortex, most neurons exhibit preferences for particular features of visual stimuli, but in general, the tuning is broad. Thus, even simple stimuli evoke responses in numerous neurons with differing but overlapping feature preferences, and it is commonly held that a particular feature is encoded in the pattern of graded responses of the activated population rather than in the optimal responses of individual cells. To decipher this population code, responses evoked by a particular stimulus need to be identified and bound together for further joint processing and must not be confounded with responses to other, nearby stimuli. Such selection of related responses could be achieved by synchronizing the respective discharges at a time scale of milliseconds, as this would selectively and jointly enhance their saliency. This hypothesis predicts that a given set of neurons should exhibit synchronized discharges more often when responding to a single stimulus than when activated by different but simultaneously presented stimuli. To test this prediction, recordings were performed with two electrodes from spatially segregated cells in the middle temporal area (MT) of the awake behaving macaque monkey. It was found that cells with overlapping receptive fields, but different preferences for directions of motion, can engage in synchronous activity if they are stimulated with a single moving bar. In contrast, if the same cells are activated with two different bars, each moving in the direction preferred by the cells at the two respective sites, responses show no or much fewer synchronous epochs. Control experiments exclude that this effect is attributable to changes in response amplitude, the mere presence of two stimuli, or the specific orientation of the bars. The critical variable determining the strength of correlation is the extent to which both sites are activated by a common stimulus or by two different stimuli with different directions of motion.
Action Potentials↗
Precise timing of neuronal discharges within and across cortical areas: implications for synaptic transmission.
Multielectrode recordings were performed in a variety of structures of structures of the mammalian brain in order to examine temporal relations among simultaneously measured neuronal responses. Data indicate close correlations between perceptual phenomena and zero-time lag synchronization of distributed neuronal discharges.
Animals↗
Stimulus dependent intercolumnar synchronization of single unit responses in cat area 17.
Recent concepts of cortical information processing suggest that visual stimuli are represented by ensembles of synchronously firing neurones. This hypothesis predicts that individual cells in separate columns of the visual cortex should synchronize their discharges in response to a single coherent stimulus and fire asynchronously when each neurone responds to a different stimulus. To test this prediction, we recorded simultaneously with two stereotrodes from single units with non-overlapping, colinearly arranged receptive fields in area 17 of the anaesthetized cat. In support of the hypothesis, cell pairs activated by the same long bar stimulus discharged in synchrony, and fired with no or diminished temporal correlation when each neurone was activated by an independent light bar.
Animals↗
Temporal coding in the visual cortex: new vistas on integration in the nervous system.
Although our knowledge of the cellular components of the cortex is accumulating rapidly, we are still largely ignorant about how distributed neuronal activity can be integrated to contribute to unified perception and behaviour. In the visual system, it is still unresolved how responses of feature-detecting neurons can be bound into representations of perceptual objects. Recent crosscorrelation studies show that visual cortical neurons synchronize their responses depending on how coherent features are in the visual field. These results support the hypothesis that temporal correlation of neuronal discharges may serve to bind distributed neuronal activity into unique representations. Furthermore, these studies indicate that neuronal responses with an oscillatory temporal structure may be particularly advantageous as carrier signals for such a temporal coding mechanism. Based on these recent findings, it is suggested here that binding of neuronal activity by a temporal code may provide a solution to the problem of integration in distributed neuronal networks.
Animals↗
Synchronization of oscillatory neuronal responses between striate and extrastriate visual cortical areas of the cat.
Recent studies have shown that neurons in area 17 of cat visual cortex display oscillatory responses which can synchronize across spatially separate orientation columns. Here, we demonstrate that unit responses recorded from the posteromedial lateral suprasylvian area, a visual association area specialized for the analysis of motion, also exhibit an oscillatory temporal structure. Cross-correlation analysis of unit responses reveals that cells in area 17 and the posteromedial lateral suprasylvian area can oscillate synchronously. Moreover, we find that the interareal synchronization is sensitive to features of the visual stimuli, such as spatial continuity and coherence of motion. These results support the hypothesis that synchronous neuronal oscillations may serve to establish relationships between features processed in different areas of visual cortex.
Animals↗
Interhemispheric synchronization of oscillatory neuronal responses in cat visual cortex.
Neurons in area 17 of cat visual cortex display oscillatory responses that can synchronize across spatially separate columns in a stimulus-specific way. Response synchronization has now been shown to occur also between neurons in area 17 of the right and left cerebral hemispheres. This synchronization was abolished by section of the corpus callosum. Thus, the response synchronization is mediated by corticocortical connections. These data are compatible with the hypothesis that temporal synchrony of neuronal discharges serves to bind features within and between the visual hemifields.
Animals↗
A low-cost single-board solution for real-time, unsupervised waveform classification of multineuron recordings.
We describe a low-cost single-board system for unsupervised, real-time spike sorting of recordings from a number of neurons on a single microelectrode. The maximum number of spike classes depends on the quality of the recording; it will typically be between 2 and 5. The spike sorter communicates with a conventional microcomputer through a standard serial port (RS232). For typical firing rates as measured in the mammalian central nervous system, this set-up will accommodate up to some 10 parallel spike sorters for as many separate microelectrodes.
Algorithms↗