posted on 2015-12-17, 00:34authored byVeena Venkatachalam, Daan Brinks, Dougal Maclaurin, Daniel Hochbaum, Joel Kralj, Adam E. Cohen
We developed a technique, “flash
memory”, to record
a photochemical imprint of the activity statefiring or not
firingof a neuron at a user-selected moment in time. The key
element is an engineered microbial rhodopsin protein with three states.
Two nonfluorescent states, D1 and D2, exist
in a voltage-dependent equilibrium. A stable fluorescent state, F,
is reached by a photochemical conversion from D2. When
exposed to light of a wavelength λwrite, population
transfers from D2 to F, at a rate determined by the D1 ⇌ D2 equilibrium. The population of F maintains
a record of membrane voltage which persists in the dark. Illumination
at a later time at a wavelength λread excites fluorescence
of F, probing this record. An optional third flash at a wavelength
λreset converts F back to D2, for a subsequent
write–read cycle. The flash memory method offers the promise
to decouple the recording of neural activity from its readout. In
principle, the technique may enable one to generate snapshots of neural
activity in a large volume of neural tissue, e.g., a complete mouse
brain, by circumventing the challenge of imaging a large volume with
simultaneous high spatial and high temporal resolution. The proof-of-principle
flash memory sensors presented here will need improvements in sensitivity,
speed, brightness, and membrane trafficking before this goal can be
realized.