Multiscale Optical Ca2+ Imaging of Tonal Organization in Mouse Auditory Cortex

Abstract

SUMMARY Spatial patterns of functional organization, resolved by microelectrode mapping, comprise a core principle of sensory cortices. In auditory cortex, however, recent two-photon Ca2+ imaging challenges this precept, as the traditional tonotopic arrangement appears weakly organized at the level of individual neurons. To resolve this fundamental ambiguity about the organization of auditory cortex, we developed multiscale optical Ca2+ imaging of unanesthetized GCaMP transgenic mice. Single-neuron activity monitored by two-photon imaging was precisely registered to large-scale cortical maps provided by transcranial wide field imaging. Neurons in the primary field responded well to tones, neighboring neurons were appreciably co-tuned, and preferred frequencies adhered tightly to a tonotopic axis. By contrast, nearby secondary-field neurons exhibited heterogeneous tuning. The multiscale imaging approach also readily localized vocalization regions and neurons. Altogether, these findings cohere electrode and two-photon perspectives, resolve new features of auditory cortex, and offer a promising approach generalizable to any cortical area.

Resting-state hemodynamics are spatiotemporally coupled to synchronized and symmetric neural activity in excitatory neurons

“…The kinetics of GCaMP3 and GCaMP6f are similar (25). High-speed wide-field imaging of GCaMP fluorescence provides a depthintegrated, ensemble measurement of neural events over a much larger field of view compared with two-photon microscopy (18,19,24,26). However, an essential consideration when using wide-field GCaMP imaging is the spectral overlap between hemoglobin absorption and GCaMP excitation and emission bands (Fig.…”

“…1A (22). Changes in GCaMP fluorescence reflect changes in intracellular calcium, and have been widely shown to correspond to neural spiking activity in studies using two-photon microscopy (22)(23)(24). The kinetics of GCaMP3 and GCaMP6f are similar (25).…”

Functional imaging of neuronal activity of auditory cortex by using Cal-520 in anesthetized and awake mice

“…Among these reasons, the use of different indicators might be animportant possibility, although this aspect seems to be often ignored in the community. The use of indicators with a low SNR and detection sensitivity, e.g., OGB-1 and GCaMP3 [14,19,20], may result in a low detection rate of responding neurons in the sensory cortex, thereby yielding an incomplete activity map. In addition, the use of fluo-4, a commonly used indicator for astrocytes [34], may cause a significant contamination of neuronal signals by astrocytes.…”

“…So far, various Ca 2+ indicators including rhod-2 [6], fura-2 [7,8], OGB-1 [9][10][11][12][13], fluo-2 [14], fluo-4 [9,15,16], Alexa Fluor 594 together with fluo-5F [17,18], and genetically encoded Ca 2+ indicators (GCaMP3 [1] and GCaMP6s [3]) [14,19,20] have been widely used in studies of the Au1 with two-photon Ca 2+ imaging in both in vitro and in vivo conditions. The in vivo experiments, particularly the functional mapping experiments, have provided important insights into the topographic organization of the Au1, but the degree of precision in tonotopic mapping has been controversial.…”

“…In addition, rapid advances in genetically encoded calcium indicators (GECIs) have provided promising tools to image Ca 2+ activity in living tissues and specific cell types in vivo. Issa et al have previously used GCaMP3 in the Au1 to address the issue of topographic organization [19]. However, its sensitivity to single action potentials and the detection rate of active neurons are both inferior to those of the synthetic indicator OGB-1 [1,3,5,36].…”