INTERACTIONS BETWEEN HIGH AND LOW FREQUENCY INPUTS IN SOMATOSENSORY CORTEX: AN IN VITRO OPTICAL IMAGING STUDY

F.J. URBANO*; E. LEZNIK; R.R. LLINAS

New York, USA

Conferencia; Optical Monitoring of activity in the brain and heart. A celebration of Merocyanine-540.; 2002

Thalamocortical dysrhytmias (TCD) are at the basis of many pathological conditions that are characterized by the increment of low frequency oscillatory activity. Such increase could be generating asymmetrical neuronal activity within the boundaries of low and high frequency oscillating cortical neurons (i.e. edge effect; Llinas et al. 1999; PNAS). Here we studied the spatiotemporal interactions between high and low frequency inputs using optical imaging of voltage-sensitive dye signals combined with field potentials and intracellular recordings. Somatosensory cortical slices from 2-5 week old rats (350-400 m thick) were stained with the voltage-sensitive dye RH795 and the fluorescent activity was recorded using a CCD camera (Fujix HRDeltaron 1700). Single or low frequency (2 to 10Hz) and high frequency (40Hz) repetitive stimulation were applied on cortical white matter. Our results indicate that a single shock was able to generate a well-defined area of cortical activation with a radially oriented columnar configuration (n=8). On the other hand, the repetitive 40Hz stimulation was rapidly restraining the activation area to a smaller radial column (n=6) in agreement with previous results (Contreras & Llinas, 2001; J. Neurosci.). When a single shock was applied during the 40Hz stimulation, spatiotemporal profiles of the single shock cortical responses were unaffected. However, there was a single shock-dependent increment of activity within deep layers at the 40Hz cortical activation area (n=5). Thus, our results suggest that high-frequency cortical activation can be modulated by low frequency inputs.