It should topoisomerase ii also be noted that the physical distance between the ferrule and the electrode array (>2 mm) suggests against any photoelectric artifacts, due to the propensity of light to scatter in neural tissue (Adamantidis et al., 2007). However, we suspected that these were a result of the Fourier decomposition of the response waveform, rather than originating in a separate neuronal process or response. In order to distinguish the roles these harmonics play in the signal compared to the primary response at the stimulation frequency, we systematically removed the harmonics from the LFP (rmlinesc.m, Chronux; Bokil et al., 2010). With this algorithm, the time-series signal is converted to frequency space, and then the spectrum

is interpolated across at the defined frequencies, removing significant sine waves from continuously recorded data without altering phase properties – as would occur with a notch filter. This has been used previously to remove the line noise resulting from nearby electronics and power sources (Viswanathan and Freeman, 2007). As we progressively removed harmonics from the LFP response to 50 mW/mm2, 7 Hz, 10 ms stimulation, the peristimulus average became increasingly sinusoidal, centered on the stimulus frequency (Figure ​Figure5B5B). The harmonics therefore play an integral role in generating the waveform of the LFP pulse response, particularly as the waveform deviates from the pure sinusoid of the stimulation frequency. FIGURE 5 Harmonic

deconstruction demonstrates their participation in non-oscillatory dynamics of the hippocampal pulse response to medial septal stimulation. Harmonics and artifacts of stimulation are not present in control subjects (A). Successively removing

… We next examined the system’s ability to detect hippocampal single-unit responses to medial septal optogenetic stimulation (Figure ​Figure66). NeuroRighter is capable of identifying and sorting units online (Newman et al., 2013). NeuroRighter can also store raw data for offline sorting, however, and so to demonstrate this capability we isolated units offline from 25 kHz sampled data using Matlab scripts combining wavelet transformation and superparamagnetic clustering (wave_clus; Quiroga et al., 2004). Two example Anacetrapib units were analyzed for waveform (Figures 6A,C) and mean firing rate (Figures 6B,D) properties before, during, and after a 50 mW/mm2, 23 Hz, 10 ms stimulus train. FIGURE 6 Hippocampal single unit firing rates increase in response to optical stimulation of the MS. Mean firing rates for two single units (A,C) identified from 50 mW/mm2, 23 Hz, 10 ms stimulation trials. Mean firing rate (B,D) tended to increase during the stimulation … In both cases the mean firing rate increased during the stimulation epoch, as calculated across several trials. The firing rate returned to baseline for the first unit (Figures 6A,B), whereas the second unit maintained the new average firing rate during the post-stimulus epoch (Figures 6C,D).