Neuronal Bases of Perceptual Learning Revealed by a Synaptic Balance Scheme

Abstract

Our ability to perceive external sensory stimuli improves as we experience the same stimulus repeatedly. This perceptual enhancement, called perceptual learning, has been demonstrated for various sensory systems, such as vision, audition, and somatosensation. I investigated the contribution of lateral excitatory and inhibitory synaptic balance to perceptual learning. I constructed a simple associative neural network model in which sensory features were expressed by the activities of specific cell assemblies. Each neuron is sensitive to a specific sensory feature, and the neurons belonging to the same cell assembly are sensitive to the same feature. During perceptual learning processes, the network was presented repeatedly with a stimulus that was composed of a sensory feature and noise, and the lateral excitatory and inhibitory synaptic connection strengths between neurons were modified according to a pulse-timing-based Hebbian rule. Perceptual learning enhanced the cognitive performance of the network, increasing the signal-to-noise ratio of neuronal activity. I suggest here that the alteration of the synaptic balance may be essential for perceptual learning, especially when the brain tries to adopt the most suitable strategy--signal enhancement, noise reduction, or both--for a given perceptual task.

Plasticity between Neuronal Pairs in Layer 4 of Visual Cortex Varies with Synapse State

“…Activation of the strongest L4-L4 connections can trigger postsynaptic spiking (Feldmeyer et al, 1999; Saez and Friedlander, 2009), propagating intralaminar synaptic activity. Within visual cortex L4, coexistence of strong stable connections with weaker plastic connections might be due to the need for L4 circuitry to remain stable during most sensory processing, allowing for dynamic behavior with altered input (Maffei et al, 2004) or during sensory learning (Calford, 2002; Hoshino, 2004; Karmarkar and Dan, 2006; Tsanov and Manahan-Vaughan, 2007; Feldman, 2009). Alternatively, plasticity may be induced only in some connections during normal sensory experience, keeping overall excitability stable.…”

Perceptual Learning via Modification of Cortical Top-Down Signals

“…First, models which intrinsically change the early stimulus representation [8–11] can explain perceptual learning only at the expense of a degradation on other tasks. A task-specific top-down input, instead, can specifically suppress or enhance a certain pre-wiring without interference with other tasks.…”

“…Perceptual learning, i.e., the change of perception following sensory experiences, is typically explained as a modification of either the feed-forward synaptic pathway to V1 [5–7], or recurrent connections within V1 [8–11] triggered by repeated practicing. Because these synaptic modifications would affect any input stream through V1, however, perceptual learning would inevitably deteriorate the information processing in other situations.…”

Where is the classic interference theory for sleep and memory?

“…Psychophysical, neuroimaging, and computational studies suggest that different brain dynamics underlie consolidation of motor and perceptual memories. While consolidation of motor learning seems to require engagement of new brain regions and increased functional connectivity in the cortico-cerebellar system for performance of the learned task (e.g., Maquet et al 2003; for a review see Ungerleider et al 2002), consolidation of perceptual learning seems to be mainly restricted to strength of local connectivity within the cortical regions initially involved in memory acquisition (e.g., Hoshino 2004;Karni & Sagi 1991;Schwartz et al 2002; for a review see Gilbert et al 2001).…”