Phase relationships between LFPs and FSI spike times leave open the question of whether FSI firing rates are modulated in relationship to LFPs. Such relationships would provide further evidence for the relevance of ventral striatal LFPs for local processing. To address this, we constructed tuning curves of firing rate as a function of gamma-50 and gamma-80 power. In order to compare sessions with different gamma power levels and neurons with different firing rates, gamma power was z-scored and firing rates were plotted as a fraction of the neuron's minimum firing rate of the raw tuning curve. Because the resulting tuning curves were generally well fit by a line, we used linear regression in order to quantify the magnitude and significance of tuning. In general, FSIs tuned to either gamma-50 power, gamma-80 power, both, or neither were observed, although the majority (31/53) were tuned to at least one. Figure 13A shows an example of a neuron that increased its firing rate with power in both gamma bands, while the neuron in Figure 13B had decreased firing with gamma-50 power but increased firing with gamma-80 power (top row). For both example neurons, gamma power did not significantly affect spike-field coherence (bottom row).
