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L Benusková

Publications and source records attributed to L Benusková.

8 recordsLinked to original sources
PubMed2001

Theory for normal and impaired experience-dependent plasticity in neocortex of adult rats.

We model experience-dependent plasticity in the cortical representation of whiskers (the barrel cortex) in normal adult rats, and in adult rats that were prenatally exposed to alcohol. Prenatal exposure to alcohol (PAE) caused marked deficits in experience-dependent plasticity in a cortical barrel-column. Cortical plasticity was induced by trimming all whiskers on one side of the face except two. This manipulation produces high activity from the intact whiskers that contrasts with low activity from the cut whiskers while avoiding any nerve damage. By a computational model, we show that the evolution of neuronal responses in a single barrel-column after this sensory bias is consistent with the synaptic modifications that follow the rules of the Bienenstock, Cooper, and Munro (BCM) theory. The BCM theory postulates that a neuron possesses a moving synaptic modification threshold, theta(M), that dictates whether the neuron's activity at any given instant will lead to strengthening or weakening of its input synapses. The current value of theta(M) changes proportionally to the square of the neuron's activity averaged over some recent past. In the model of alcohol impaired cortex, the effective theta(M) has been set to a level unattainable by the depressed levels of cortical activity leading to "impaired" synaptic plasticity that is consistent with experimental findings. Based on experimental and computational results, we discuss how elevated theta(M) may be related to (i) reduced levels of neurotransmitters modulating plasticity, (ii) abnormally low expression of N-methyl-d-aspartate receptors (NMDARs), and (iii) the membrane translocation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in adult rat cortex subjected to prenatal alcohol exposure.

Action Potentials↗
PubMed2000

The intra-spine electric force can drive vesicles for fusion: a theoretical model for long-term potentiation.

We have estimated the intensity of intra-spine electric fields triggered by stimulation of excitatory spine synapses. We show that this electric force can cause fast electrophoretic movement of negatively charged vesicles which bring new postsynaptic receptors and membrane for insertion during the induction of long-term potentiation (LTP). Due to the direction of an intra-spine electric field, movement of vesicles is electrophoretically directed along the longitudinal spine axis towards the spine head. Thus, the number of fused vesicles may be proportional not only to the increased calcium concentration within the spine head during the induction of LTP but also to the magnitude of electric force which drives vesicles towards the postsynaptic membrane.

Animals↗
PubMed1999

Computational study of experience-dependent plasticity in adult rat cortical barrel-column.

We model experience-dependent plasticity in the adult rat S1 cortical representation of the whiskers (the barrel cortex) which has been produced by trimming all whiskers on one side of the snout except two. This manipulation alters the pattern of afferent sensory activity while avoiding any direct nerve damage. Our simplified model circuitry represents multiple cortical layers and inhibitory neurons within each layer of a barrel-column. Utilizing a computational model we show that the evolution of the response bias in the barrel-column towards spared whiskers is consistent with synaptic modifications that follow the rules of the Bienenstock, Cooper and Munro (BCM) theory. The BCM theory postulates that a neuron possesses a dynamic synaptic modification threshold, thetaM, which dictates whether the neuron's activity at any given instant will lead to strengthening or weakening of the synapses impinging on it. However, the major prediction of our model is the explanation of the delay in response potentiation in the layer-IV neurons through a masking effect produced by the thresholded monotonically increasing inhibition expressed by either the logarithmic function, h(x) = mu log(1 + x), or by the power function, h(x) = mu x(0.8-0.9), where mu is a constant. Furthermore, simulated removal of the supragranular layers (layers II/III) reduces plasticity of neurons in the remaining layers (IV-VI) and points to the role of noise in synaptic plasticity.

Animals↗
PubMed1998

Hypothetical neural mechanism that may play a role in mental rotation: an attractor neural network model.

We propose an attractor neural network (ANN) model that performs rotation-invariant pattern recognition in such a way that it can account for a neural mechanism being involved in the image transformation accompanying the experience of mental rotation. We compared the performance of our ANN model with the results of the chronometric psychophysical experiments of Cooper and Shepard (Cooper L A and Shepard R N 1973 Visual Information Processing (New York: Academic) pp 204-7) on discrimination of alphanumeric characters presented in various angular departures from their canonical upright position. Comparing the times required for pattern retrieval in its canonical upright position with the reaction times of human subjects, we found agreement in that (i) retrieval times for clockwise and anticlockwise departures of the same angular magnitude (up to 180 degrees) were not different, (ii) retrieval times increased with departure from upright and (iii) increased more sharply as departure from upright approached 180 degrees. The rotation-invariant retrieval of the activity pattern has been accomplished by means of the modified algorithm of Dotsenko (Dotsenko V S 1988 J. Phys. A: Math. Gen. 21 L783-7) proposed for translation-, rotation- and size-invariant pattern recognition, which uses relaxation of neuronal firing thresholds to guide the evolution of the ANN in state space towards the desired memory attractor. The dynamics of neuronal relaxation has been modified for storage and retrieval of low-activity patterns and the original gradient optimization of threshold dynamics has been replaced with optimization by simulated annealing.

Algorithms↗
PubMed1994

Dynamic synaptic modification threshold: computational model of experience-dependent plasticity in adult rat barrel cortex.

Previous electrophysiological experiments have documented the response of neurons in the adult rat somatic sensory ("barrel") cortex to whisker movement after normal experience and after periods of experience with all but two whiskers trimmed close to the face (whisker "pairing"). To better understand how the barrel cortex adapts to changes in the flow of sensory activity, we have developed a computational model of a single representative barrel cell based on the Bienenstock, Cooper, and Munro (BCM) theory of synaptic plasticity. The hallmark of the BCM theory is the dynamic synaptic modification threshold, theta M, which dictates whether a neuron's activity at any given instant will lead to strengthening or weakening of the synapses impinging on it. The threshold theta M is proportional to the neuron's activity averaged over some recent past. Whisker pairing was simulated by setting input activities of the cell to the noise level, except for two inputs that represented untrimmed whiskers. Initially low levels of cell activity, resulting from whisker trimming, led to low values for theta M. As certain synaptic weights potentiated, due to the activity of the paired inputs, the values of theta M increased and after some time their mean reached an asymptotic value. This saturation of theta M led to the depression of some inputs that were originally potentiated. The changes in cell response generated by the model replicated those observed in in vivo experiments. Previously, the BCM theory has explained salient features of developmental experience-dependent plasticity in kitten visual cortex. Our results suggest that the idea of a dynamic synaptic modification threshold, theta M, is general enough to explain plasticity in different species, in different sensory systems, and at different stages of brain maturity.

Animals↗
PubMed1991

Antidepressants and synaptic plasticity: a hypothesis.

The assumption is introduced that there are two types of adaptive responses in central neurons in response to significantly changed circuit activity. Morphological synaptic modifications and synapse turnover are thought to be involved in both of these responses, in such a way that in the first case they are to restore the circuit activity level as it was in the past, and in the second case they are to switch it to a new pattern. The events eliciting synaptogenesis are proposed to be different in these instances. The role of compensatory extrasynaptic receptors insertion and preferential insertion of synaptic receptors induced by enhanced presynaptic activity are discussed. The hypothesis as to how these two adaptive responses come into action during depression and antidepressant treatment is then proposed.

Adaptation, Physiological↗