Limits...
Coding efficiency of fly motion processing is set by firing rate, not firing precision.

Spavieri DL, Eichner H, Borst A - PLoS Comput. Biol. (2010)

Bottom Line: Although these two environmental variables have a considerable impact on the fly's nervous system, they do not impede the fly to behave suitably over a wide range of conditions.We found that the mean firing rate, but not firing precision, changes with temperature, while both were affected by mean luminance.Because we also found that information rate and coding efficiency are mainly set by the mean firing rate, our results suggest that, in the face of environmental perturbations, the coding efficiency is improved by an increase in the mean firing rate, rather than by an increased firing precision.

View Article: PubMed Central - PubMed

Affiliation: Department of System and Computational Neurobiology, Max-Planck-Institute of Neurobiology, Martinsried, Germany.

ABSTRACT
To comprehend the principles underlying sensory information processing, it is important to understand how the nervous system deals with various sources of perturbation. Here, we analyze how the representation of motion information in the fly's nervous system changes with temperature and luminance. Although these two environmental variables have a considerable impact on the fly's nervous system, they do not impede the fly to behave suitably over a wide range of conditions. We recorded responses from a motion-sensitive neuron, the H1-cell, to a time-varying stimulus at many different combinations of temperature and luminance. We found that the mean firing rate, but not firing precision, changes with temperature, while both were affected by mean luminance. Because we also found that information rate and coding efficiency are mainly set by the mean firing rate, our results suggest that, in the face of environmental perturbations, the coding efficiency is improved by an increase in the mean firing rate, rather than by an increased firing precision.

Show MeSH
Firing rate and precision as a function of temperature and light intensity.A Mean firing rate. B Spike jitter, measured as the standard deviation of the first spike after a velocity transient (from negative to positive). C Average Fano factors for transient responses 50 ms after a velocity transition, calculated in an interval of 50ms, using overlapping windows of 20 ms. Color code represents the linear interpolation of the mean values at the experimental points, indicated by the crosses. Q and K are the temperature and luminance coefficients, respectively (for details see text). Error bars are bootstrap confidence intervals (, 1000 replications) D Top: Segment of a stimulus waveform during a velocity transition from inhibitory to excitatory direction. Center: Raster plots of the responses in 20 trials at three different conditions, indicated in the legends. Each mark represents the occurrence of one spike. Bottom: Distributions of the arrival time of the first spike for the three different conditions shown above, obtained using a kernel density estimator with optimized width for Gaussian distributions.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2908696&req=5

pcbi-1000860-g002: Firing rate and precision as a function of temperature and light intensity.A Mean firing rate. B Spike jitter, measured as the standard deviation of the first spike after a velocity transient (from negative to positive). C Average Fano factors for transient responses 50 ms after a velocity transition, calculated in an interval of 50ms, using overlapping windows of 20 ms. Color code represents the linear interpolation of the mean values at the experimental points, indicated by the crosses. Q and K are the temperature and luminance coefficients, respectively (for details see text). Error bars are bootstrap confidence intervals (, 1000 replications) D Top: Segment of a stimulus waveform during a velocity transition from inhibitory to excitatory direction. Center: Raster plots of the responses in 20 trials at three different conditions, indicated in the legends. Each mark represents the occurrence of one spike. Bottom: Distributions of the arrival time of the first spike for the three different conditions shown above, obtained using a kernel density estimator with optimized width for Gaussian distributions.

Mentions: In order to quantify the effect of temperature and luminance on the various response properties like firing rate and reliability, we calculated for each luminance a temperature coefficient Q (the ratio of the respective response parameter at 25C and 15C). A strong influence of temperature expresses itself in a Q value different from 1 at many different luminance levels. Furthermore, we calculated at each temperature a luminance coefficient, K, as the ratio of the response parameter at 100 cd m and at 0.1 cd m. Again, a strong influence of luminance on a given response property is revealed by K values different from 1 at many different temperatures. Both temperature and luminance have a strong effect on the mean firing rate of H1, with Q and K values of up to 3 (Fig. 2A). However, temperature has almost no effect on the response reliability while luminance does (Fig. 2 B–D). We quantified the response reliability in two different ways: first, we measured the standard deviation (STD) of the occurrence times of the first spike after a velocity transition, i.e. a zero-crossing from an inhibitory to an excitatory direction of motion (Fig. 2D). This measure should, at least in principle, be independent of the mean firing rate. Second, we measured the response reliability 50 ms after a velocity transition using the ratio of the variance of the spike count and the mean spike count (Fano Factor) within a 20 ms time window (Fig. 2C). Here, a better response reliability can be achieved in two ways - a smaller variance or a higher firing rate associated with the refractory period of the neuron [32]. The effect of temperature on the STD or on the Fano Factor is rather small: at almost all light intensities tested, the coefficients of temperature (Q) are not statistically different from 1 (Fig. 2B,C). In contrast, the reliability of the response improves considerably for all measures of reliability (all p0.001, Wilcoxon test) with increasing luminance. The coefficient of luminance (K) reaches values smaller than 0.5 at several temperatures measured. These findings are summarized by the Spearman correlation coefficients between response properties and temperature and luminance (Table 1). In summary, we find that temperature does not significantly affect the response reliability, while higher luminance values increase the response reliability substantially (Figs. 2 B,C).


Coding efficiency of fly motion processing is set by firing rate, not firing precision.

Spavieri DL, Eichner H, Borst A - PLoS Comput. Biol. (2010)

Firing rate and precision as a function of temperature and light intensity.A Mean firing rate. B Spike jitter, measured as the standard deviation of the first spike after a velocity transient (from negative to positive). C Average Fano factors for transient responses 50 ms after a velocity transition, calculated in an interval of 50ms, using overlapping windows of 20 ms. Color code represents the linear interpolation of the mean values at the experimental points, indicated by the crosses. Q and K are the temperature and luminance coefficients, respectively (for details see text). Error bars are bootstrap confidence intervals (, 1000 replications) D Top: Segment of a stimulus waveform during a velocity transition from inhibitory to excitatory direction. Center: Raster plots of the responses in 20 trials at three different conditions, indicated in the legends. Each mark represents the occurrence of one spike. Bottom: Distributions of the arrival time of the first spike for the three different conditions shown above, obtained using a kernel density estimator with optimized width for Gaussian distributions.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2908696&req=5

pcbi-1000860-g002: Firing rate and precision as a function of temperature and light intensity.A Mean firing rate. B Spike jitter, measured as the standard deviation of the first spike after a velocity transient (from negative to positive). C Average Fano factors for transient responses 50 ms after a velocity transition, calculated in an interval of 50ms, using overlapping windows of 20 ms. Color code represents the linear interpolation of the mean values at the experimental points, indicated by the crosses. Q and K are the temperature and luminance coefficients, respectively (for details see text). Error bars are bootstrap confidence intervals (, 1000 replications) D Top: Segment of a stimulus waveform during a velocity transition from inhibitory to excitatory direction. Center: Raster plots of the responses in 20 trials at three different conditions, indicated in the legends. Each mark represents the occurrence of one spike. Bottom: Distributions of the arrival time of the first spike for the three different conditions shown above, obtained using a kernel density estimator with optimized width for Gaussian distributions.
Mentions: In order to quantify the effect of temperature and luminance on the various response properties like firing rate and reliability, we calculated for each luminance a temperature coefficient Q (the ratio of the respective response parameter at 25C and 15C). A strong influence of temperature expresses itself in a Q value different from 1 at many different luminance levels. Furthermore, we calculated at each temperature a luminance coefficient, K, as the ratio of the response parameter at 100 cd m and at 0.1 cd m. Again, a strong influence of luminance on a given response property is revealed by K values different from 1 at many different temperatures. Both temperature and luminance have a strong effect on the mean firing rate of H1, with Q and K values of up to 3 (Fig. 2A). However, temperature has almost no effect on the response reliability while luminance does (Fig. 2 B–D). We quantified the response reliability in two different ways: first, we measured the standard deviation (STD) of the occurrence times of the first spike after a velocity transition, i.e. a zero-crossing from an inhibitory to an excitatory direction of motion (Fig. 2D). This measure should, at least in principle, be independent of the mean firing rate. Second, we measured the response reliability 50 ms after a velocity transition using the ratio of the variance of the spike count and the mean spike count (Fano Factor) within a 20 ms time window (Fig. 2C). Here, a better response reliability can be achieved in two ways - a smaller variance or a higher firing rate associated with the refractory period of the neuron [32]. The effect of temperature on the STD or on the Fano Factor is rather small: at almost all light intensities tested, the coefficients of temperature (Q) are not statistically different from 1 (Fig. 2B,C). In contrast, the reliability of the response improves considerably for all measures of reliability (all p0.001, Wilcoxon test) with increasing luminance. The coefficient of luminance (K) reaches values smaller than 0.5 at several temperatures measured. These findings are summarized by the Spearman correlation coefficients between response properties and temperature and luminance (Table 1). In summary, we find that temperature does not significantly affect the response reliability, while higher luminance values increase the response reliability substantially (Figs. 2 B,C).

Bottom Line: Although these two environmental variables have a considerable impact on the fly's nervous system, they do not impede the fly to behave suitably over a wide range of conditions.We found that the mean firing rate, but not firing precision, changes with temperature, while both were affected by mean luminance.Because we also found that information rate and coding efficiency are mainly set by the mean firing rate, our results suggest that, in the face of environmental perturbations, the coding efficiency is improved by an increase in the mean firing rate, rather than by an increased firing precision.

View Article: PubMed Central - PubMed

Affiliation: Department of System and Computational Neurobiology, Max-Planck-Institute of Neurobiology, Martinsried, Germany.

ABSTRACT
To comprehend the principles underlying sensory information processing, it is important to understand how the nervous system deals with various sources of perturbation. Here, we analyze how the representation of motion information in the fly's nervous system changes with temperature and luminance. Although these two environmental variables have a considerable impact on the fly's nervous system, they do not impede the fly to behave suitably over a wide range of conditions. We recorded responses from a motion-sensitive neuron, the H1-cell, to a time-varying stimulus at many different combinations of temperature and luminance. We found that the mean firing rate, but not firing precision, changes with temperature, while both were affected by mean luminance. Because we also found that information rate and coding efficiency are mainly set by the mean firing rate, our results suggest that, in the face of environmental perturbations, the coding efficiency is improved by an increase in the mean firing rate, rather than by an increased firing precision.

Show MeSH