Attention modulates synchronized neuronal firing in primate somatosensory cortex
A potentially powerful information processing strategy in the brain is to take
advantage of the temporal structure of neuronal spike trains. An increase in
synchrony within the neural representation of an object or location increases the
efficacy of that neural representation at the next synaptic stage in the brain;
thus, increasing synchrony is a candidate for the neural correlate of attentional
selection. We investigated the synchronous firing of pairs of neurons in the
secondary somatosensory cortex (SII) of three monkeys trained to switch attention
between a visual task and a tactile discrimination task. We found that most
neuron pairs in SII cortex fired synchronously and, furthermore, that the degree
of synchrony was affected by the monkey's attentional state. In the monkey
performing the most difficult task, 35% of neuron pairs that fired synchronously
changed their degree of synchrony when the monkey switched attention between the
tactile and visual tasks. Synchrony increased in 80% and decreased in 20% of
neuron pairs affected by attention.
This reseach is described in:
Steinmetz, P. N., Roy, A., Fitzgerald, P., Hsiao, S. S., Johnson, K. O., and
Niebur, E. (2000). Attention Modulates Synchronized Neuronal Firing in Primate
Somatosensory Cortex. Nature, 404, 187--190.
also see:
Niebur E, Hsiao SS, Johnson KO. (2002) Synchrony: a neuronal mechanism
for attentional selection? Current Opinion in Neurobiology, 12 (2),
190-194.
People Involved:
Peter Steinmetz, Arup Roy
Paul Fitzgerald, Steve Hsiao
Ken Johnson, Ernst Niebur
Electrophysiological correlates of synchronous neural activity and attention: a short review
Attentional selection implies preferential treatment of some sensory
stimuli over others. This requires differential representation of
attended and unattended stimuli. Most previous research has focused on
pure rate codes for this representation but recent evidence indicates
that a mixed code, involving both mean firing rate and temporal codes,
may be employed. Of particular interest is a distinction of attended
from unattended stimuli based on synchrony within neural
populations. I review electrophysiological evidence at macroscopic,
mesoscopic and microscopic spatial scales showing that the degree of
synchronous activity varies with the attentional state of the
perceiving organism.
Niebur, E. (2002). Electrophysiological correlates of synchronous neural
activity and attention: a short review. Biosystems, 67 (1-3), 157-166.
The effects of input rate and synchrony on a coincidence detector: Analytical solution
We derive analytically the solution for the output rate of the ideal
coincidence detector. The solution is for an arbitrary number of input
spike trains with identical binomial count distributions (which
includes Poisson statistics as a special case) and identical arbitrary
pairwise cross-correlations, from zero correlation (independent
processes) to complete correlation (identical processes).
Mikula, S. and Niebur, E. (2003). The effects of input rate and synchrony on a
coincidence detector: Analytical solution. Neural Computation, 15(3),
539-47.
People involved:
Shawn Mikula
Ernst Niebur
Synaptic depression leads to nonmonotonic frequency dependence in the coincidence detector
In this report, we extend our previous analytical results
(Mikula and Niebur03a) for the coincidence detector by taking into
account probabilistic frequency-dependent synaptic depression. We
present a solution for the steady-state output rate of an ideal
coincidence detector receiving an arbitrary number of input spike
trains with identical binomial count distributions (which includes
Poisson statistics as a special case) and identical arbitrary pairwise
cross-correlations, from zero correlation (independent processes) to
perfect correlation (identical processes). Synapses vary their
efficacy probabilistically according to the observed depression
mechanisms. Our results show that synaptic depression, if made
sufficiently strong, will result in an inverted U-shaped curve for the
output rate of a coincidence detector as a function of input
rate. This leads to the counterintuitive prediction that higher
presynaptic (input) rates may lead to lower postsynaptic (output)
rates where the output rate may fall faster than the inverse of the
input rate.
Mikula, S. and Niebur, E. (in press). Synaptic depression leads to nonmonotonic
frequency dependence in the coincidence detector. Neural
Computation.
People involved:
Shawn Mikula
Ernst Niebur
Chaos control
Over the past 50 years, non-linear property of a single neuron has
been extensively studied. These studies elucidated geometrical
interpretation of neuronal action potential, its quasi-periodicity and
chaotic transition. Under highly irregular input regime in cortical
activities, if the deterministic characteristics have relevant
significance in neuronal information processing is unknown. Yet, many
researchers pointed out the deterministic (chaotic) behavior in EEG
signal. Given that there is some sort of deterministic process in
neuronal signal, we seek possibility to control it by external
stimuli(1). Current focus is to apply the theory to stabilize higher
order biologically inspired dynamical system and show the method is
applicable to the large-scale biological system such as brain.
1: Schuster HG, Niebur E, Hunt ER, Johnson GA, Locher M. Parametric
feedback resonance in chaotic systems. Phys Rev Lett. 1996
Jan 15;76(3):400-403.
People Involved:
Hideaki Shimazaki
Ernst Niebur
Stimulus-induced synchronization of neurons that encode objects
The neural mechanisms that allow the binding of different features in a
complex
visual scene to a certain object (for example, "blue" and
"four-cornered"
to code a blue square) is still a very much discussed question. It has been
shown that cells in V1 and V2 encode feature-object relationships such as
"border
ownership".
Thus, the cells have to exchange information with other neurons encoding
distant parts of the same figure. One theory concerning the binding problem
is the so-called "Correlation Hypothesis" (von der Malsburg,
1981), which
postulates a stimulus-induced synchronization of neurons that encode
different
aspects of the same perceived object. We test this hypothesis by analyzing
the activity of simultaneously recorded pairs of neurons in the macaque
visual
cortex with several combined or independent static stimuli (i.e. geometric
figures), and measuring the amount of excess synchronization in the evoked
spike trains.
Hartmut Schuetze is PostDoc since
02/2002 in both the Niebur
and the von der
Heydt Labs, and evaluates spike train data from double recordings.
He also is involved in psychophysical experiments on object-related visual
aftereffects.
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