Local Versus Global Effects of Isoflurane Anesthesia on Visual Processing in the Fly Brain

Abstract

What characteristics of neural activity distinguish the awake and anesthetized brain? Drugs such as isoflurane abolish behavioral responsiveness in all animals, implying evolutionarily conserved mechanisms. However, it is unclear whether this conservation is reflected at the level of neural activity. Studies in humans have shown that anesthesia is characterized by spatially distinct spectral and coherence signatures that have also been implicated in the global impairment of cortical communication. We questioned whether anesthesia has similar effects on global and local neural processing in one of the smallest brains, that of the fruit fly (Drosophila melanogaster). Using a recently developed multielectrode technique, we recorded local field potentials from different areas of the fly brain simultaneously, while manipulating the concentration of isoflurane. Flickering visual stimuli (‘frequency tags’) allowed us to track evoked responses in the frequency domain and measure the effects of isoflurane throughout the brain. We found that isoflurane reduced power and coherence at the tagging frequency (13 or 17 Hz) in central brain regions. Unexpectedly, isoflurane increased power and coherence at twice the tag frequency (26 or 34 Hz) in the optic lobes of the fly, but only for specific stimulus configurations. By modeling the periodic responses, we show that the increase in power in peripheral areas can be attributed to local neuroanatomy. We further show that the effects on coherence can be explained by impacted signal-to-noise ratios. Together, our results show that general anesthesia has distinct local and global effects on neuronal processing in the fruit fly brain.

Isoflurane Impairs Low-Frequency Feedback but Leaves High-Frequency Feedforward Connectivity Intact in the Fly Brain

“…We analyzed local field potentials (LFPs) data previously recorded from the brains of awake and anesthetized flies (Cohen et al, 2016). Whereas Cohen et al (2016) focused on visually evoked responses, here we focus on the analysis of power, coherence, and GC of spontaneous LFPs, and how these are affected by isoflurane.…”

“…Whereas Cohen et al (2016) focused on visually evoked responses, here we focus on the analysis of power, coherence, and GC of spontaneous LFPs, and how these are affected by isoflurane. In this section, we briefly recap the experimental setup.…”

“…In this section, we briefly recap the experimental setup. For the full experimental details, see Cohen et al (2016).…”

“…1 A , B ). The effects of isoflurane were tested at concentrations of 0% and 0.6% (for details, see Cohen et al, 2016). An olfactory stimulus controller was used to deliver six air puffs to gauge the behavioral responsiveness of the flies in each concentration of isoflurane.…”

“…Fly movement activity in response to the air puff was recorded with a camera. We used the video data to confirm that 0.6% isoflurane abolished the behavioral responsiveness and that behavioral responsiveness returned after recovery (Cohen et al, 2016). …”