Abstract
Transcranial magnetic stimulation (TMS) noninvasively interferes with human cortical function, and is widely used as an effective technique for probing causal links between neural activity and cognitive function. However, the physiological mechanisms underlying TMS-induced effects on neural activity remain unclear. We examined the mechanism by which TMS disrupts neural activity in a local circuit in early visual cortex using a computational model consisting of conductance-based spiking neurons with excitatory and inhibitory synaptic connections. We found that single-pulse TMS suppressed spiking activity in a local circuit model, disrupting the population response. Spike suppression was observed when TMS was applied to the local circuit within a limited time window after the local circuit received sensory afferent input, as observed in experiments investigating suppression of visual perception with TMS targeting early visual cortex. Quantitative analyses revealed that the magnitude of suppression was significantly larger for synaptically-connected neurons than for isolated individual neurons, suggesting that intracortical inhibitory synaptic coupling also plays an important role in TMS-induced suppression. A conventional local circuit model of early visual cortex explained only the early period of visual suppression observed in experiments. However, models either involving strong recurrent excitatory synaptic connections or sustained excitatory input were able to reproduce the late period of visual suppression. These results suggest that TMS targeting early visual cortex disrupts functionally distinct neural signals, possibly corresponding to feedforward and recurrent information processing, by imposing inhibitory effects through intracortical inhibitory synaptic connections.
Highlights
Neural activity represents information about our perception and behavior
Models either involving strong recurrent excitatory synaptic connections or sustained excitatory input were able to reproduce the late period of visual suppression. These results suggest that Transcranial magnetic stimulation (TMS) targeting early visual cortex disrupts functionally distinct neural signals, possibly corresponding to feedforward and recurrent information processing, by imposing inhibitory effects through intracortical inhibitory synaptic connections
We examined TMS-induced suppression of spiking activity using a local circuit model of early visual cortex
Summary
Neural activity represents information about our perception and behavior. One effective method for investigating the relationship between neural activity and such functions is to manipulate neural activity and assess effects on the functions. Mechanisms other than direct suppression of feedforward neural activity may be involved in TMS-induced visual suppression (Boyer et al 2005; Lamme 2006; Koivisto et al 2010) Another candidate explanation for TMS-induced interference is based on interaction between stimulated neurons (Miyawaki and Okada 2004a, b). A previous computational study (Miyawaki and Okada 2004a, b) analyzed TMS-induced interference on a local cortical circuit, but it was based on limited analyses of the equilibrium state of an idealized analog neuron network model that did not represent spiking membrane dynamics of realistic neurons. We examined how spiking activity was perturbed by TMS applied to the local circuit model Using this approach, we quantitatively analyzed TMS-induced interference with neural activity, regarding the involvement of synaptic interaction and feedback input, while manipulating synaptic weights and afferent input properties
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