Attention and working memory: a dynamical model of neuronal activity in the prefrontal cortex (original) (raw)
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Spatial working memory allows one to temporarily store the spatial information for use. Previous studies have shown that spatial working memory impairment is influenced by aging, for both human and some animal species. In this paper, we modelled and analyzed the Delayed Response Task, a spatial working memory task performed on monkeys of various age groups to assess the effects of aging on the pyramidal neurons in the dorsolateral prefrontal cortex (dlPFC). Different from the models introduced in the supplementary material in Professor Weaver's paper, we used a less excitable activation function for the inhibitory neurons. Specifically, we compared the number of points that maintained tuned persistent activity to the original stimulus location at 0 (TPA-S) under different conditions, and compared the synaptic weight distributions across the 6-dimensional space in LHS projections under different conditions.
Emergent properties of the prefrontal cortical circuit for working memory processing
IEEE SMC'99 Conference Proceedings. 1999 IEEE International Conference on Systems, Man, and Cybernetics (Cat. No.99CH37028)
In the monkey brain performing a spatial working memory task, tuned activity of the prefrontal cortical neurons that is sustained during the delay period is a neuronal substrate of the working memory. The sustainment of the activity would be attributable to the intrinsic dynamics of the prefrontal cortical circuit because the cue input, which triggers the dynamics, is turned off and no additional external input is provided in the delay period. To understand the intrinsic dynamics of the prefrontal cortical circuit, I here show the computer simulations of a model prefrontal cortical circuit with biologically plausible leaky integrate-and-fire neurons. The excitatory (inhibitory) synaptic inputs to the pyramidal cells whose preferred directions are close to the cue direction increased (decreased respectively) gradually while receiving the cue-related input and remained high (low respectively) during the delay period. The, opposing effects were observed for the pyramidal cells whose preferred directions are almost anti-parallel to the cue direction. These simulations suggest that the tuned excitatory and inhibitory synaptic inputs are formed in the prefrontal cortical circuit. These synaptic inputs persist even after the termination of the cue-related input, accounting for the tuned delay-period activity for spatial working memory.
A model of prefrontal cortex dopaminergic modulation during the delayed alternation task
Journal of Cognitive Neuroscience, 2002
& Working memory performance is modulated by the level of dopamine (DA) D1 receptors stimulation in the prefrontal cortex (PFC). This modulation is exerted at different time scales. Injection of D1 agonists/antagonists exerts a longlasting influence (several minutes or hours) on PFC pyramidal neurons. In contrast, during performance of a cognitive task, the duration of the postsynaptic effect of phasic DA release is short lasting. The functional relationships of these two time scales of DA modulation remain poorly understood. Here we propose a model that combines these two time scales of DA modulation on a prefrontal neural network. The model links the cellular and behavioral levels during performance of the delayed alternation task. The network, which represents the activity of deep-layer pyramidal neurons with intrinsic neuronal properties, exhibits two stable states of activity that can be switched on and off by excitatory inputs from long-distance cortical areas arriving in superficial layers. These stable states allow PFC neurons to maintain representations during the delay period. The role of an increase of DA receptors stimulation is to restrict inputs arriving on the prefrontal network. The model explains how the level of working memory performance follows an inverted U-shape with an increased stimulation of DA D1 receptors. The model predicts that (1) D1 receptor agonists increase perseverations, (2) D1 antagonists increase distractability, and (3) the duration of the postsynaptic effect of phasic DA release in the PFC is adjusted to the delay period of the task. These results show how the precise duration of the postsynaptic effect of phasic DA release influences behavioral performance during a simple cognitive task. &
Dopaminergic Regulation of Neuronal Circuits in Prefrontal Cortex
Neuromodulators, like dopamine, have considerable influence on the processing capabilities of neural networks. This has for instance been shown in the working memory functions of prefrontal cortex, which may be regulated by altering the dopamine level. Experimental work provides evidence on the biochemical and electrophysiological actions of dopamine receptors, but there are few theories concerning their significance for computational properties , (Hasselmo, 1994b)). We point to experimental data on neuromodulatory regulation of temporal properties of excitatory neurons and depolarization of inhibitory neurons, and suggest computational models employing these effects. Changes in membrane potential may be modelled by the firing threshold, and temporal properties by a parameterization of neuronal responsiveness according to the preceding spike interval. We apply these concepts to two examples using spiking neural networks. In the first case, there is a change in the input synchronization of neuronal groups, which leads to changes in the formation of synchronized neuronal ensembles. In the second case, the threshold of interneurons influences lateral inhibition, and the switch from a winner-take-all network to a parallel feedforward mode of processing. Both concepts are interesting for the modeling of cognitive functions and may have explanatory power for behavioral changes associated with dopamine regulation.
A spiking network model of short-term active memory
The Journal of …, 1993
Studies of cortical neurons in monkeys performing shortterm memory tasks have shown that information about a stimulus can be maintained by persistent neuron firing for periods of many seconds after removal of the stimulus. The mechanism by which this sustained activity is initiated and maintained is unknown. In this article we present a spiking neural network model of short-term memory and use it to investigate the hypothesis that recurrent, or "re-entrant," networks with constant connection strengths are sufficient to store graded information temporarily.
A neurocomputational theory of the dopaminergic modulation of working memory functions
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1999
The dopaminergic modulation of neural activity in the prefrontal cortex (PFC) is essential for working memory. Delay-activity in the PFC in working memory tasks persists even if interfering stimuli intervene between the presentation of the sample and the target stimulus. Here, the hypothesis is put forward that the functional role of dopamine in working memory processing is to stabilize active neural representations in the PFC network and thereby to protect goal-related delay-activity against interfering stimuli. To test this hypothesis, we examined the reported dopamine-induced changes in several biophysical properties of PFC neurons to determine whether they could fulfill this function. An attractor network model consisting of model neurons was devised in which the empirically observed effects of dopamine on synaptic and voltage-gated membrane conductances could be represented in a biophysically realistic manner. In the model, the dopamine-induced enhancement of the persistent Na+...
Synaptic dynamics and decision making
Proceedings of the National Academy of Sciences, 2010
During decision making between sequential stimuli, the first stimulus must be held in memory and then compared with the second. Here, we show that in systems that encode the stimuli by their firing rate, neurons can use synaptic facilitation not only to remember the first stimulus during the delay but during the presentation of the second stimulus so that they respond to a combination of the first and second stimuli, as has been found for "partial differential" neurons recorded in the ventral premotor cortex during vibrotactile flutter frequency decision making. Moreover, we show that such partial differential neurons provide important input to a subsequent attractor decisionmaking network that can then compare this combination of the first and second stimuli with inputs from other neurons that respond only to the second stimulus. Thus, both synaptic facilitation and neuronal attractor dynamics can account for sequential decision making in such systems in the brain.