Measuring Sharp Waves and Oscillatory Population Activity With the Genetically Encoded Calcium Indicator GCaMP6f

Area of Science:

• Neuroscience
• Biophysics
• Molecular Biology

Background:

• Genetically encoded calcium indicators (GECIs) like GCaMP6f are crucial for monitoring neuronal activity.
• Previous studies have primarily focused on cellular-level activity, with less exploration of population-level detection capabilities.

Purpose of the Study:

• To assess the sensitivity of GCaMP6f for detecting population activity during sparse neuronal firing, comparable to local field potential (LFP) sensitivity.
• To evaluate the temporal resolution of GCaMP6f for capturing fast network oscillations vital for memory processes.

Main Methods:

• Simultaneous local field potential (LFP) and optical GCaMP6f fluorescence recordings were performed in Thy1-GCaMP6f mouse hippocampal slices.
• The study analyzed sharp waves (SWs), carbachol-induced theta oscillations, and interictal-like spikes to assess signal detection and frequency response.

Main Results:

• GCaMP6f detected population activity during SWs with a 0.3% ΔF/F signal, correlating with LFP but with a 40.3 ms delay.
• Population GCaMP6f signals accurately tracked 20 Hz stimulation and detected oscillations up to 40 Hz with reduced amplitude.
• GCaMP6f showed a significant amplitude increase (28.9x) between SWs and theta bursts, compared to LFP (2.4x).

Conclusions:

• GCaMP6f is sensitive enough for detecting synchronous network events with sparse firing and sub-threshold activity.
• Population GCaMP6f signals are adequate for monitoring theta and beta oscillations (<25 Hz).
• GCaMP6f offers advantages over LFP, including non-contact recording and freedom from stimulation artifacts, beneficial for high-throughput and artifact-sensitive applications.