William R. Softky's research while affiliated with National Institutes of Health and other places
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Publications (13)
1. In neocortical slices, the majority of neurons fire quite regularly in response to constant current injections. But neurons in the intact animal fire irregularly in response to constant current injection as well as to visual stimuli. 2. To quantify this observation, we developed a new measure of variability, which compares only adjacent interspi...
1. In neocortical slices, the majority of neurons fire quite regularly in response to constant current injections. But neurons in the intact animal fire irregularly in response to constant current injection as well as to visual stimuli. 2. To quantify this observation, we developed a new measure of variability, which compares only adjacent interspi...
One measure of the computational power of a single unit in a network is the rate at which it can transfer information. Because that rate depends both on the unit's analog resolution and on its speed, many types of units may reach their optimum information flow when they operate very fast, with only coarse or binary resolution at each time step (thi...
McCulloch and Pitts originally thought that cortical neurons computed using single spikes, with temporal resolution well under a millisecond. But the most popular current simplification of those neurons is as devices which perform computations based on real-valued firing rates, averaged over many spikes and over much longer times. However, single-s...
Transmission of information is an important function of cortical neurons, so it is conceivable that they have evolved to transmit information efficiently, with low noise and high temporal precision. Such precision is consistent with the output generated by various working models that mimick neuronal activity, from simple integrate-and-fire models t...
A thalamic relay cell may act as a comparator, sending the brain the difference between sensory input and a dynamic, anticipatory prediction of it. Such predictive inhibition would implement several useful perceptual principles: nonlinear reduced-redundancy coding in space and time; compensation for feedback's inevitable processing and propagation...
Simulations of a morphologically reconstructed cortical pyramidal cell suggest that the long, thin, distal dendrites of such a cell may be ideally suited for nonlinear coincidence-detection at time-scales much faster than the membrane time-constant. In the presence of dendritic sodium spiking conductances, such hypothetical computations might occur...
How random is the discharge pattern of cortical neurons? We examined recordings from primary visual cortex (V1; Knierim and Van Essen, 1992) and extrastriate cortex (MT; Newsome et al., 1989a) of awake, behaving macaque monkey and compared them to analytical predictions. For nonbursting cells firing at sustained rates up to 300 Hz, we evaluated two...
When a typical nerve cell is injected with enough current, it fires a regular stream of action potentials. But cortical cells in vivo usually fire irregularly, reflecting synaptic input from presynaptic cells as well as intrinsic biophysical properties. We have applied the theory of stochastic
processes to spike trains recorded from cortical neuron...
The Hebbian neural learning algorithm that implements Principal Component Analysis (PCA) can be extended for the analysis of more realistic forms of neural data by including higher than two-channel correlations and non-Euclidean 1p metrics. Maximizing a dth rank tensor form which correlates d channels is equivalent to raising the exponential order...
Citations
... Lacey et al.[15] reported a similar mean value of 7.1 Hz firing in layer 5 motor cortex cells at rest, from micro-electrode recordings in rats. CVs of spiking activity in cortical neurons have been consistently reported in previous literature as being close to 1[75,76].Based on these experimentally reported values, the firing rates of the neural network model with random connectivity were closer to the physiological range, though with slightly higher firing in layer 2/3 and lower in 6. The local connectivity model showed an increase in mean firing rates over all the neuron populations and a wider range in mean CV. ...
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... According to the rate encoding hypothesis, which dates back to Adrian and Zotterman [1], the information is represented by the number of spikes within an appropriate time window, irrespective of their temporal distribution. However, both experimental results and theoretical considerations suggest that the complexity of the neural code goes beyond this simple scheme [2,3]. ...
... They designed higher order neural networks with translation invariant properties and experimented on the classic Exclusive-OR and TC problem. Softsky ( [17]) explored correlations in high dimensions using Hebbian learning algorithm. ...
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... Increasingly we understand the brain to be the device that makes predictions of the external environment and reacts with corresponding actions [19,20]. Sensory inputs from anatomical structures like the eyes, nose, and ears are able to collect real data about the outside world and relay unprocessed raw information to the brain [21]. As one goes through life, certain expectations of the way things should be are created; these are predictions that are built from past experience. ...
... Here phase coding converts from numeric inputs to delayed spiking signals similar to, but simpler than, that defined by Gautrais and Thorpe (1998). Our phase coding is also consistent with the neural spike codes described by Softky (1996), especially when k = 2, except that our spikes are not necessarily irregular or Poisson distributed. When a neuron fires, its output signal could also contain amplitude or rate-coded information, but these types of information coding are not used in the spiking algorithms we present here. ...
... It does not depend on the prior history of the point process. In some cases, the description of neuronal activity with a Poisson process is experimentaly approved [16][17][18] but in many others both experimental data [19][20][21][22] and theoretical considerations [24] exclude a possibility for a neuronal activity to have a Poisson statistics. ...
... Although the changes in baseline conduction velocity are relatively small, considering the long distances that axons traverse in the brain, HCN channels can be expected to change the arrival time of the action potential by, for example, 0.5 ms in the case of unmyelinated cerebellar parallel fibers (assuming 3 mm length and 0.3 m/s velocity; Swadlow and Waxman, 2012). Such temporal delays will influence information processing in the central nervous system, because spike-timing dependent plasticity (Caporale and Dan, 2008), coincidence detection (Softky, 1994), and the neuronal rhythms of cell ensembles (Buzsáki et al., 2013) precisely tune the arrival times of action potentials. There are several examples of the specific tuning of conduction velocity in the sub-millisecond domain: the diameter and the degree of myelination of cerebellar climbing fibers (Sugihara et al., 1993;Lang and Rosenbluth, 2003; but see Baker and Edgley, 2006), the degree of myelination of thalamocortical axons (Salami et al., 2003), and the internode distance of auditory axons (Ford et al., 2015) are all tuned exactly to offset the different arrival times of action potentials with a temporal precision of~100 ms. ...
... The mammalian brain is in a state of perpetual ongoing activity characterized by high levels of irregularity in single-neuron response (1,2) and correlated fluctuations across brain regions (3)(4)(5)(6)(7). Understanding the origin and functional significance of such neuronal activity has been challenging for both physics and neuroscience, and diverse competing hypotheses have been proposed to rationalize its nature. ...
... To focus on PC intrinsic excitability and to rule out network contributions, excitatory and inhibitory synaptic transmissions were pharmacologically blocked. PC discharges were evaluated using the mean ring frequency (measurement of the mean ISI) and the CV2, which estimates the variability of the ring pattern between two consecutive ISIs [55,56]. At 22 weeks, no difference in the ring properties of PCs located in lobule VI was detected between WT and SCA7 mice. ...
