Figure 4.

The gain exerted by the cortex in auditory thalamic neurons depends on their ability to signal a deviance from previous stimulation context. Scatterplots of the CSI (control condition) vs. the difference in firing rate between the control and cool conditions (spikes/stimulus difference) in response to the standard (upper panel) and deviant stimulus (lower panel), for each neuron. Blue, green, and red dots represent the neurons that were localized to the ventral (n = 12), dorsal (n = 24), and medial (n = 9) subdivisions of the MGB, respectively (n = 45, neurons that were localized to one of the three MGB subdivision). Gray dots represent MGB neurons that were not localized to a specific MGB subdivisions (n = 3). In both plots, positive values (above the horizontal line at the origin) indicate a reduction in firing rate with cortical deactivation (neurons receive facilitatory cortical influences), whereas negative values (bellow the horizontal line) indicate an increment in firing rate with cortical deactivation (neurons receive suppressive influences from the cortex). The difference in firing rate was inversely correlated with CSI for both standard and deviant stimuli. The slopes of the standard and deviant regression lines are not significantly different from each other [ANCOVA: main effect of stimuli, F_(1,92) = 1.89, p = 0.172; main effect of CSI, F_(1,92) = 43.27, p = 0; interaction, F_(1,92) = 0.23, p = 0.634; n = 48], indicating that the correlation coefficients between standard and deviant are not different. The AC differentially affects the discharge rate of neurons depending on their SSA level. Neurons without SSA are mainly facilitated, whereas some neurons with high SSA are suppressed by the cortex. AC, auditory cortex; MGB, medial geniculate body; MGV, ventral subdivision of the MGB; MGD, dorsal subdivision of the MGB; MGM, medial subdivision of the MGB; SSA, stimulus specific adaptation; CSI, common SSA index; Adapted from Antunes and Malmierca (2011).