Michael Lin, MD PhD

And these insights from imaging fast interneuron spiking over several days is something that only genetically encoded voltage indicators can provide.

Thus interneurons do learn, but there is a hierarchy of specificity, where pyramidals > PV > SST. And the role of PV appears to be to engage in negative feedback to enhance contrast between odor-encoding pyramidals, required to link the memory of CS and US, vs non-encoding pyramidals.

Interestingly they could use ASAP3 to record spiking responses of the same neurons over days, before and after training, allowing them to show that about half of the PV interneurons that respond to odor one day remain responsive the next day. Pyramidals learn more stably, SST interneurons worse.

They find that PV neurons are activated by stimulus presentation to overall suppress pyramidal spiking for a few seconds. The effect is to reduce background spiking allowing odor-specific and time-specific pyramidal cell firing to show more contrast over background.

And now the 3rd paper this week using ASAP-family voltage indicators in mice to look at fast neuronal activity.

In this case, collaborators Jiannis Taxidis and Peyman Golshani used ASAP3 to record spiking in PV and SST interneurons in the hippocampus.

Published yesterday in @natneuro.nature.com

I think it's been pushed by journal editors looking for citation metrics, but reviewers should try to push back on this trend with critical thinking.

Anyway I will get off the soap box now.

Computer calculations were thought to be resource-unlimited, but the energy demands of AI mean that is no longer true. And the odd thing is that science has always been resource-limited, so this shift toward one expensive description over multiple mechanistic investigations is self-defeating.

Of course it's not the technology itself that is to blame, but poor training and lack of selectivity in its use. In science that means reviewers and journal editors choosing to accept expensive high-throughput surveys of biology and rejecting experiments that will generate new mechanistic insights.

We see it in the overuse of energy-intensive AI for simple queries, the writing of overly long and sloppy code by AI, the overuse of high-throughput sequencing methods to generate data in lieu of any mechanistic discovery, etc.

A negative side-effect of technological abundance is that it does not train people to deal with resource-limited conditions. Growing up with the easy ability to produce productivity outputs, people lose appreciation for, and ability to identify, creative and economically resourceful solutions.

Thanks; indeed electrical signals propagate and decay in unexpected ways on length-scales from microns to meters, so there's a lot to learn

Thanks, maybe I should say most of the visible surface area in the field of view, since the axon rapidly leaves the field of view

DRG voltage imaging was performed by 1-photon confocal microscopy, confirming the high SNR of ASAP4 and extending the cell types and imaging modalities with which ASAP-family GEVIs have been used with.

This study was mostly done by our collaborator Yushin Kim at UT San Antonio; congrats to Yushin!

GCaMP3 failed to find statistically different responses in the neuropathic pain state. It's not clear why, but it could be that calcium primarily picks up large spike bursts, as we showed in the original ASAP4 study, while hypersensitivity may result in a higher frequency of smaller bursts.

Here, ASAP4e reported firing in the dorsal root ganglia (cell bodies of touch-sensing neurons) upon light touch and pressure stimuli. ASAP43 also reported larger responses after neuropathic pain is induced immunologically (complete Freund's adjuvant) or neurologically (sciatic nerve constriction).

Imaging sensory transmission and neuronal plasticity in primary sensory neurons with a positively tuned voltage indicator - Nature Communications Genetically encoded voltage indicators (GEVIs) enable fast tracking of membrane voltage in live neurons. Here, the authors use soma-targeted ASAP4.4-Kv to visualize electrical activity in sensory gang...

This was with ASAP3; our newer ASAP5 should improve responses by another 2-fold.

The second paper uses positively tuned ASAP4e (ASAP4.4) to examine how sensory neurons alter firing patterns in a model of neuropathic pain.

www.nature.com/articles/s41...

The overall message is that GFP-based ASAP voltage indicators provide high brightness, speed, and response amplitudes and genetic targetability, so that fast voltage events such as gamma oscillations can be studied without too much trouble.

ASAP3 ("PV-INs" and green in other plots) also picks up 30-70Hz gamma waves in the cortex upon visual stimulation, whereas an opsin-based indicator (red) did not, apparently due to slower responses.

It's also nice to see our mRuby2 and CyOFP being useful in the brain as non-toxic orange-red FPs.

Theta waves arise during exploration and entrain the spiking of pyramidal neurons to facilitate the emergence of place-specific encoding in the hippocampus. ASAP3 mesoscale imaging in the hippocampus finds that theta waves propagate in 1 direction in excitatory neurons, but 2 in inhibitory neurons.

Our collaborators in the Schnitzer lab have now used pan-membrane ASAP3 (which predominantly measures dendritic voltages as dendrites are most of the cell surface area in neurons) to visualize how theta waves propagate in the hippocampus.

Two voltage imaging studies in two days using ASAP fluorescent indicators.

First, visualizing electrical brain waves with ASAP3, in Cell. Free link below. Though recorded by EEG for 100 years, how brain waves arise from different neuron types has been unclear.

authors.elsevier.com/sd/article/S...

Worse than frustrating. Punishing hard work and good ideas.

Here Are the Nearly 2,500 Medical Research Grants Canceled or Delayed by Trump (Gift Article) Some cuts have been starkly visible, but the country’s medical grant-making machinery has also radically transformed outside the public eye.

New powerful article up in the New York Times on cancelled and delayed grants

www.nytimes.com/interactive/...

So lesson is, if you have a good idea, don't even bother with NIGMS. I don't know why they bother sponsoring R21s if they're not going to take a 2% score.

BTW it was NIGMS and some are guessing I have too much funding. But we're below GMS' "significant existing funds" status, and the PO will only say there are factors other than existing funding.

BTW one grant ends the same month this was going to start, taking us further below that status.

Received a 2% (top 2%) score on a NIH R21 grant last fall, and it won't get funded.

This decision was made before the new administration, actually, showing that NIH has not lived up to its mission to fund the best science for a while. It's only going to get worse now with the budget cuts.

Research in Ruin: Slashing the NIH Will Stifle Development of Lifesaving Medical Treatments and Harm the Economy Please join the Center for American Progress for the next in a series of virtual events highlighting the impact that DOGE’s cuts are having on the lives of everyday Americans; this event will focus on...

We had a tremendous conversation about these NIH cuts at @americanprogress.bsky.social with @hardeepsinghmd.bsky.social + @michaelzlin.bsky.social + @cdmenefee.bsky.social + @thehowie.bsky.social that was as timely in early April as it is today

www.americanprogress.org/events/resea...

The system used to compensate for that by an ethic of rewarding credit to originality, trained into a generation of leaders who saw new ideas truly push forward the boundaries of the known, but originality is now increasingly seen as adding risk when resources are already insufficient to go around.

The buffer for imagination (time and funds deployable to new ideas) is shrinking.

Cranking out more of the same has a natural advantage at grant or paper review time because more people understand it and the risk of failure is low, so the expected amount of risk-adjusted probability is high.

It's good for society in the short term (super-efficient) but terrible for researchers. And I would argue there is a cost for society in the long-term too, as good ideas don't get pursued because it would take so long to get a paper published that you'd run out of grant money before then.