How can the interaction between theoretical neuro-scientists and their experimental counterparts be improved? This article discusses a number of suggestions relating to the presentation of data in experimental studies...
How can the interaction between theoretical neuro-scientists and their experimental counterparts be improved? This article discusses a number of suggestions relating to the presentation of data in experimental studies. In particular, published data should account for the diversity of response properties encountered, rather than concentrating on the 'representative' response, as well as emphasizing the stochastic nature of neurons by routinely including raw, unprocessed data from individual trials, which show the degree of variability prior to averaging.
Compartmental simulations of an anatomically characterized cortical pyramidal cell were carried out to study the integrative behavior of a complex dendritic tree. Previous theoretical (Feldman and Ballard 1982;Durbin ...
Compartmental simulations of an anatomically characterized cortical pyramidal cell were carried out to study the integrative behavior of a complex dendritic tree. Previous theoretical (Feldman and Ballard 1982;Durbin and Rumelhart 1989;Mel 1990;Mel and Koch 1990;Poggio and Girosi 1990) and compartmental modeling (Koch et al. 1983;Shepherd et al. 1985;Koch and Poggio 1987;Rall and Segev 1987;Shepherd and Brayton 1987, Shepherd et al. 1989;Brown et al. 1991) work had suggested that multiplicative interactions among groups of neighboring synapses could greatly enhance the processing power of a neuron relative to a unit with only a single global firing threshold. This issue was investigated here, with a particular focus on the role of voltage-dependent N-methyl-D-asparate (NMDA) channels in the generation of cell responses. First, it was found that when a large proportion of the excitatory synaptic input to dendritic spines is carried by NMDA channels, the pyramidal cell responds preferentially to spatially clustered, rather than random, distributions of activated synapses. Second, based on this mechanism, the NMDA-rich neuron is shown to be capable of solving a nonlinear pattern discrimination task. We propose that manipulation of the spatial ordering of afferent synaptic connections onto the dendritic arbor is a possible biological strategy for pattern information storage during learning.
The real time computation of motion from real images using a single chip with integrated sensors is a hard problem. We present two analog VLSI schemes that use pulse domain neuromorphic circuits to compute motion. Pul...
ISBN:
(纸本)9781558602748
The real time computation of motion from real images using a single chip with integrated sensors is a hard problem. We present two analog VLSI schemes that use pulse domain neuromorphic circuits to compute motion. Pulses of variable width, rather than graded potentials, represent a natural medium for evaluating temporal relationships. Both algorithms measure speed by timing a moving edge in the image. Our first model is inspired by Reichardt's algorithm in the fly and yields a non-monotonic response vs. velocity curve. We present data from a chip that implements this model. Our second algorithm yields a monotonic response vs. velocity curve and is currently being translated into silicon.
Simplified models of the lateral geniculate nucles (LGN) and striate cortex illustrate the possibility that feedback to the LGN may be used for robust, low-level pattern analysis. The information fed back to the LGN i...
ISBN:
(纸本)9781558602748
Simplified models of the lateral geniculate nucles (LGN) and striate cortex illustrate the possibility that feedback to the LGN may be used for robust, low-level pattern analysis. The information fed back to the LGN is rebroadcast to cortex using the LGN's full fan-out, so the cortex→LGN→cortex pathway mediates extensive cortico-cortical communication while keeping the number of necessary connections small.
The standard theory of a leaky integrator with stochastic spike input predicts that cortical cells should fire regularly. We tested interspike-interval histograms from awake, behaving macaque visual cortex (V1 and MT)...
The standard theory of a leaky integrator with stochastic spike input predicts that cortical cells should fire regularly. We tested interspike-interval histograms from awake, behaving macaque visual cortex (V1 and MT), and found high levels of variability (CV>0.5) characteristic of a nearly random (Poisson) process. A simple integrate-and-fire model, using accepted biophysical parameters, fails by more than a factor of ten to account for the high CV. We also simulated a biophysically detailed compartment-model of an anatomically reconstructed and physiologically characterized layer V pyramidal cell; again, at high firing rate, CV values are low, in disagreement with the data. Only a few situations could account for this discrepency: very large EPSP’s, a very short membrane time constant (τm<0.3 msec), highly synchronized input, or spikes in excitable dendrites. Our analysis suggests that cortical computation may occur at a time-scale much faster than previously realized.
We analyze the dynamic behavior of large two-dimensional systems of limit-cycle oscillators with random intrinsic frequencies that interact via time-delayed nearest-neighbor coupling. We find that even small delay tim...
We analyze the dynamic behavior of large two-dimensional systems of limit-cycle oscillators with random intrinsic frequencies that interact via time-delayed nearest-neighbor coupling. We find that even small delay times lead to a novel form of frequency depression where the system decays to stable states which oscillate at a delay and interaction-dependent reduced collective frequency. For greater delay or tighter coupling between oscillators we find metastable synchronized states that we describe analytically and numerically.
Biological retinas extract spatial and temporal features in an attempt to reduce the complexity of performing visual tasks. We have built and tested a silicon retina which encodes several useful temporal features foun...
ISBN:
(纸本)9781558602229
Biological retinas extract spatial and temporal features in an attempt to reduce the complexity of performing visual tasks. We have built and tested a silicon retina which encodes several useful temporal features found in vertebrate retinas. The cells in our silicon retina are selective to direction, highly sensitive to positive contrast changes around an ambient light level, and tuned to a particular velocity. Inhibitory connections in the null direction perform the direction selectivity we desire. This silicon retina is on a 4.6 × 6.8mm die and consists of a 47 × 41 array of photoreceptors.
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