A Normalization Model of Attentional Modulation of Single Unit Responses

Although many studies have shown that attention to a stimulus can enhance the responses of individual cortical sensory neurons, little is known about how attention accomplishes this change in response. Here, we propose that attention-based changes in neuronal responses depend on the same response normalization mechanism that adjusts sensory responses whenever multiple stimuli are present. We have implemented a model of attention that assumes that attention works only through this normalization mechanism, and show that it can replicate key effects of attention. The model successfully explains how attention changes the gain of responses to individual stimuli and also why modulation by attention is more robust and not a simple gain change when multiple stimuli are present inside a neuron's receptive field. Additionally, the model accounts well for physiological data that measure separately attentional modulation and sensory normalization of the responses of individual neurons in area MT in visual cortex. The proposal that attention works through a normalization mechanism sheds new light a broad range of observations on how attention alters the representation of sensory information in cerebral cortex

ITBS-induced LTP-like plasticity parallels oscillatory activity changes in the primary sensory and motor areas of macaque monkeys

Recently, neuromodulation techniques based on the use of repetitive transcranial magnetic stimulation (rTMS) have been/nproposed as a non-invasive and efficient method to induce in vivo long-term potentiation (LTP)-like aftereffects. However,/nthe exact impact of rTMS-induced perturbations on the dynamics of neuronal population activity is not well understood./nHere, in two monkeys, we examine changes in the oscillatory activity of the sensorimotor cortex following an intermittent/ntheta burst stimulation (iTBS) protocol. We first probed iTBS modulatory effects by testing the iTBS-induced facilitation of/nsomatosensory evoked potentials (SEP). Then, we examined the frequency information of the electrocorticographic signal,/nobtained using a custom-made miniaturised multi-electrode array for electrocorticography, after real or sham iTBS. We/nobserved that iTBS induced facilitation of SEPs and influenced spectral components of the signal, in both animals. The latter/neffect was more prominent on the h band (4–8 Hz) and the high c band (55–90 Hz), de-potentiated and potentiated/nrespectively. We additionally found that the multi-electrode array uniformity of b (13–26 Hz) and high c bands were also/nafflicted by iTBS. Our study suggests that enhanced cortical excitability promoted by iTBS parallels a dynamic reorganisation/nof the interested neural network. The effect in the c band suggests a transient local modulation, possibly at the level of/nsynaptic strength in interneurons. The effect in the h band suggests the disruption of temporal coordination on larger/nspatial scales