Ben Kanter
The TransmitterThe technique, which measures calcium currents as a proxy for neuronal firing, sometimes reports unusual and potentially misleading waves of activity in the hippocampus.
By @avaskham
Albert CardonaCommentary of:
"Aberrant hippocampal Ca2+ micro-waves following synapsin-dependent adeno-associated viral expression of Ca2+ indicators" by Masala et al. 2024.
Redish Lab@thetransmitter @avaskham
@albertcardona
Calcium imaging is not a proxy for neural firing and should never be used as such. Calcium imaging (when done right*) is a biological signal that provides useful data. But calcium imaging and neural firing should be treated as separate signals providing different information about the underlying complex biological process.
* Like neural recording, calcium imaging is a hard technique to do well, and has become easy to do poorly.
If these calcium waves are actually waves in calcium, but not neural firing, then they are still a potentially important neural signal. Are these related to calcium waves in the astrocytes, as shown in retina? (e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2409971/)
As a colleague pointed out to me - imagine if calcium imaging had been developed first and so once neural recording was discovered, everyone was required to convolve their neural spikes with an exponential function to make it look more like calcium imaging. 😳
Propagation of Intercellular Calcium Waves in Retinal Astrocytes and Müller Cells
Intercellular Ca[2+] waves are believed to propagate through networks of glial cells in culture in one of two ways: by diffusion of IP[3] between cells through gap junctions or by release of ATP, which functions as an extracellular messenger. Experiments ...
Spencer LaVere Smith@adredish @thetransmitter @avaskham @albertcardona I mostly agree with the sentiment, but I would stop short of saying “never”.
In some cases the correlation is pretty strong and clear, and better than other correlations the field regularly makes use of. In other cases it is a very different signal.
Using calcium signals as a proxy for neuronal activity can be defensible in some cases. Rigor is key.