Aim: 

Transcranial magnetic stimulation (TMS) modifies the excitability of cortical cells depending on the stimulus parameters. We have previously shown for both X and Y LGN cells that sustained responses to flashed spots were reduced after application of TMS at 1Hz on primary visual cortex (V1). Under these stimulation parameters no changes were observed on transient responses. Here we show, using a more detailed experimental approach, that TMS@1Hz induces subtle effects on transient responses depending on the LGN cell type.

Methods: 

Experiments were performed in anesthetized and paralyzed adult cats. Procedures were in keeping with the guidelines given by the International Council for Laboratory Animal Science and the European Union (statute nr 86/809). Visual stimulation (flashed bright and dark bars) was used to build the spatiotemporal receptive fields (eRF) of LGN neurons extracellularly recorded, both under control conditions and during the simultaneous application of TMS on V1.

Results: 

X cells (n = 18) did show an increase in the latency to maximal response (mean = 1 msec, p < 0.05) and a decrease in firing rate (mean = 10%, p < 0.005). Analysis of the eRF shapes suggests that these changes were due to an increase in the rate between peripheral and central amplitudes. Y cells (n = 25) showed no changes regarding the spatiotemporal structure. Subsequent intervalogram analysis confirmed the results.

Conclusions: 

These results indicate the existence of different cortical effects on X and Y cells transient response.

Supported by MEC and Xunta de Galicia (Consellería de Educación)