Population data is complex: the relationship between burst firing, spike adaptation, and attentional modulation in macaque Area V4
Distinguishing between different neural cell classes can provide value insight into circuit mechanisms, but remains a challenge in extracellular recordings. One approach has been to characterize differences in the physiological properties of identified neuronal cell types, and then apply these physiological distinctions towards inferring neuronal identity in extracellular recordings. For example, intracellular studies have shown that the ability to fire action potentials of short duration is restricted to classes of neurons that express specific ion channels. This difference in action potential shape has allowed numerous studies to distinguish between narrow spiking (putative interneurons) and broad spiking (putative pyraxiv midal) neurons. Here, I extend this approach by considering how burst firing and spike adaptation can provide additional insight into neural identity, and use these metrics to account for heterogeneity in the electrophysiological correlates of attention across individual neurons in macaque Area V4. I begin by characterizing spike amplitude, duration, and frequency adaptation. I find that when I divide the population into broad and narrow spiking groups, there is significantly greater action potential amplitude and frequency adaptation among broad spiking neurons. This finding provides further validation of the use of spike waveform duration as a method to distinguish between cortical cell classes, and as discussed in the final chapter, may provide a glimpse into the depolarization state of neurons across different attention conditions. In addition to characterizing spike adaptation, I characterize the burst spiking behavior of V4 neurons. I find that burstiness varies considerably across the population, but did not find evidence for distinct classes of burst behavior. Burstiness did, however, vary more widely across the class of neurons that show the greatest heterogeneity in attentional modulation, and within that class, burstiness helped account for differences in attentional modulation. Among these broad spiking neurons, rate modulation was largely restricted to bursty neurons, which as a group showed a highly significant increase in firing rate with attention. Further work will need to determine whether this relationship between attentional modulation and burstiness reflects a difference in the intrinsic excitability of these neurons or whether it reflects differences in the inputs they receive.