Population imaging of ongoing neuronal activity in the visual cortex of awake rats

Abstract

It is unclear how the complex spatiotemporal organization of ongoing cortical neuronal activity recorded in anesthetized animals relates to the awake animal. We therefore used two-photon population calcium imaging in awake and subsequently anesthetized rats to follow action potential firing in populations of neurons across brain states, and examined how single neurons contributed to population activity. Firing rates and spike bursting in awake rats were higher, and pair-wise correlations were lower, compared with anesthetized rats. Anesthesia modulated population-wide synchronization and the relationship between firing rate and correlation. Overall, brain activity during wakefulness cannot be inferred using anesthesia.

Visually evoked activity in cortical cells imaged in freely moving animals

“…All neurons displayed robust Ca 2ϩ -transients (Fig. 3G), which were similar to action potential (AP)-induced transients measured by conventional MP microscopes in anesthetized (5,6,9) and awake (8,11) animals. Transients in astrocytes were of similar amplitude (peak ⌬F/F 0 of 20-30%) but much slower dynamics (rise times of 2-15 s, durations of 5-100 s; Fig.…”

“…For the remaining frames, lateral displacements were quantified by using the imaging data (16 displacements estimated per image frame) and corrected by using an algorithm described previously (27). The detected brain displacements were well within the correctable range of the motion correction algorithm (27) and were similar in amplitude and frequency of occurrence to those observed in awake head-fixed animals (8,11). Brain displacements were weakly but significantly correlated to the animal's velocity and acceleration (Fig.…”

“…To quantify the observed changes in neuronal activity, we applied an algorithm for automated AP detection (8) to fluorescence recorded by using the fiberscope. Because the fiberscope does not (yet) allow concurrent single-cell electrical recordings, a direct quantification of the AP detection probability and of the falsepositive detection rate is not possible.…”

“…Previously, this approach, which includes both allothetic and idiothetic cues, lead to the discovery of place cells (1), head-direction cells (2), and grid cells (3). Multiphoton (MP) imaging (4) of neurons bulk-loaded with calcium indicators (5-7) allows not only the unambiguous identification and precise anatomical localization of active neurons but also the simultaneous recording of activity in multiple neurons even at very low firing rates (8)(9)(10). Although one major limitation of conventional MP imaging has been the need to firmly hold the skull in position to prevent the brain from moving relative to the microscope objective, some aspects of free movement can be simulated in head-fixed animals by placing them in a virtual reality situation (11).…”

Information Routing, Correspondence Finding, and Object Recognition in the Brain

“…Note, however, that while V1 cells respond similarly in awake and anesthetized animals, it is nearly impossible to drive IT cells under anesthesia (for recent results on the large differences between general neuron responses in awake and anesthetized animals, see e.g. Greenberg et al 2008). So the very complex effective RFs of IT cells in awake animals cannot directly correspond to anatomical RFs, since then they should respond similarly also under anesthesia.…”