Variability Of Neuronal Responses Research Articles

A multitrial analysis for revealing significant corticocortical networks in magnetoencephalography and electroencephalography

We present an MEG/EEG framework to reveal statistically significant brain areas engaged in the same cognitive process across trials without resort to averaging procedures. The variability of neuronal responses is assumed to take place only in the reconstructed time series of cortical sources and not in their positions. This hypothesis allows the use of the surrogate data method to detect recurrently active brain areas across trials adjusted with any cortically constrained focal MEEG inverse solution. Results obtained from synthetic data show that considering several trials enhances the accuracy of the source localisation. We apply this approach on MEG data recorded during a simple visual stimulation. The considered stimulus is frequency tagged in order to reveal the neural network correlated to its perception using phase synchronisation analysis. The results show consistent patterns of distributed synchronous networks centred on occipital areas.

Temporally asymmetric Hebbian learning and neuronal response variability

Recent experimental data have characterized a form of long-term synaptic modification that depends on the relative timing of pre- and post-synaptic action potentials. Modeling studies indicate that this rule can automatically adjust excitatory synaptic strengths so that the post-synaptic neuron receives roughly equal amount of excitation and inhibition and as a consequence fires irregular spike trains as observed in vivo. This rule also induces competition between different inputs and strengthens groups of synapes that are correlated over short time periods.

Temporal integration vs. parallel processing: coping with the variability of neuronal messages in directional hearing of insects.

The behaviour of many animals indicates a high precision in the processing of sensory signals, which often seems at odds with the large variability of individual neuronal responses. Using the directional hearing of the grasshopper Chorthippus biguttulus (Ch. biguttulus) as a model system, we investigated the possible contributions of temporal integration and parallel processing at the receptor level to the observed behavioural acuity. The precision of the animals' phonotactic orientation behaviour to stimuli of different durations was measured and compared with the spiking responses of auditory receptor cells, leading to the following results. A behavioural decision based on integrating the spikes from a pair of receptors (one cell in each ear) over a 1000-ms time window would substantially decrease the error probability, compared with evaluating a 250-ms period. The animal as a whole, however, responded as precisely to a 250 ms stimulus as to a stimulus of natural duration (c. 1000 ms). A phonotactic decision based on a 1.5 dB intensity difference between the ears corresponds to a spike count difference of approximately 1 spike per 100 ms in a pair of receptors. As these differences are in the order of the statistical spike count fluctuations, the error probabilities for an ideal observer of the spike count are substantially higher (13-18%) than the errors observed in the behavioural tests (only 5%). We conclude that the animals' nervous system has to sample information from a pool of 6-13 receptors to arrive at the observed behavioural precision.

Effects of attention on the reliability of individual neurons in monkey visual cortex.

To determine the physiological mechanisms underlying the enhancement of performance by attention, we examined how attention affects the ability of isolated neurons to discriminate orientation by investigating the reliability of responses with and without attention. Recording from 262 neurons in cortical area V4 while two rhesus macaques did a delayed match-to-sample task with oriented stimuli, we found that attention did not produce detectable changes in the variability of neuronal responses but did improve the orientation discriminability of the neurons. We also found that attention did not change the relationship between burst rate and response rate. Our results are consistent with the idea that attention selects groups of neurons for a multiplicative enhancement in response strength.

Response Variability of Neurons in Primary Visual Cortex (V1) of Alert Monkeys

Response variability of neurons limits the reliability and resolution of sensory systems. It is generally thought that response variability in the visual system increases at cortical levels, but the causes of the variability have not been identified. We have measured the response variability of neurons in primary visual cortex (V1) of alert monkeys. We recorded from 80 single cells distributed over all V1 layers and from 8 parvocellular cells of the lateral geniculate nucleus. All cells were stimulated with a bar of near-optimal orientation, color, and dimensions while continuously monitoring the eye movements of fixation. To minimize the effects of eye movements, responses that occurred while the eye was relatively steady were selected for analysis. The impulses elicited by each stimulus presentation were counted, and the variance and coefficient of variation were computed. Both measures of response variability were much lower than reported previously for V1 cells of both alert and anesthetized monkeys. Our data show that fixational eye movements cause a large component of response variance in alert monkeys. Moreover, the reliability of V1 neurons is not obviously degraded compared with lateral geniculate nucleus cells. The high reliability of neurons in alert monkeys is consistent with expectations from conventional biophysical models, and it suggests that activity in a modest number of neurons may suffice to form a perceptual decision.

The response variability of striate cortical neurons in the behaving monkey.

In order to relate single cell performance to behavioral discrimination one needs measurements of the response variance of the units. We recorded from 183 single units of area V1 of monkeys performing an orientation discrimination task. The response variance was found to increase with increasing response strength. This relationship between response variance and response strength was well described by a power function with a power close to one. The response variance was on average 1.9 times the response strength. Despite important differences in preparation, the behaving monkey data are in good agreement with those previously obtained in paralysed and anesthetised animals.

Visual and oculomotor functions of monkey substantia nigra pars reticulata. III. Memory-contingent visual and saccade responses.

Visual and oculomotor functions of monkey substantia nigra pars reticulata. III. Memory-contingent visual and saccade responses.

Short-term response variability of monkey striate neurons

Short-term response variability of monkey striate neurons