This is real team science: 5 labs expert in recordings from mouse and monkey cerebellum joined forces to make the project happen. Thanks to a great team, led by @1DanaCohen1, @Steve_Lisberger, @dkneurolab , @theHullLab, @Neuralcomplab, and Javier Medina.

Second, the recruitment of this non-coding pool by optogenetic stimulation can enhance perception. This means that this latent pool of neurons (the “dark matter”) can actually be useful for sensory processing!

We therefore provide two key new insights into the mechanism and significance of sparse coding. First, the sparse code is enforced by selective targeting of powerful inhibition, which predominantly suppresses non-coding neurons.

The all-optical experiments also revealed that these non-coding (i.e. normally silent) neurons are selectively targeted by inhibition recruited during sensory stimulation – in other words, they are preferentially suppressed by sensory stimulation.

All-optical interrogation revealed that we can produce a behavioral bias which depends on the number of neurons activated. Moreover, what is fascinating is that the behavioral effect is dominated by activation of non-coding neurons.

Next, we switched to all-optical interrogation to be able to activate small ensembles of identified neurons using two-photon optogenetics, and measure the impact both on local network activity and on behavior.

We then performed two-photon imaging during the task and confirmed that coding of whisker input is sparse – in other words, most neurons are silent! This sparse code aligns with work from many groups (e.g. Olshausen & Field, Brecht, Helmchen, Svoboda, Barth & Poulet).

We used one-photon optogenetics to show that barrel cortex is required for this task and that the processing window is very brief – less than 100 ms!

We developed a challenging new behavioral task for mice which requires that they integrate bilateral whisker information. This produces sigmoidal psychometric curves, similar to the classical curves in visual psychophysics experiments (Shadlen, Newsome, Movshon, et al.).

Most neurons in the cortex remain silent, even during sensory stimulation and behavior. What are these silent neurons good for? This is known as the “dark matter problem” of the brain. We address this problem in our @NeuroCellPress study led by @omgauld doi.org/10.1016/j.neuron.202…