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A new pre-print from my lab! We asked whether intrinsic plasticity in the midbrain merely adjusts neuronal spiking up and down, or whether it can also tune neurons temporally, to either long or short synaptic inputs. TLDR: Yes, they are tuned! biorxiv.org/content/10.110… (thread 1/n)
Tectum (aka superior colliculus in mammals) is one of those regions with a distributed sensory network, organized in a map. Neurons aren't oscillatory, like in STG or spinal cord, so people usually pay more attention to synaptic plasticity than to intrinsic properties. 2/n
But we thought: what if neurons also care about the LENGTH of synaptic inputs? We used dynamic clamp to simulated inputs of diff length, and neurons did care: some spiked more to short synaptic activation, while some preferred longer currents. Neurons were temporally tuned! 3/n
OK, now what if we show our animals (Xenopus tadpoles) some short visual events (flashes), or longer events (looming-like transitions). All things being equal, will neurons adjust? And if yes, how? Will they become MORE, or less responsive to whatever they saw? 4/n
Here's a program we used for stimulation: faculty.bard.edu/~akhakhal/chec… ; you can click the link, and see the same thing tadpoles saw (for 4 hours). By default it does "flashes", but if you put "1000" in the "Transition phase" field on the left, you'll get trippy "looming" stimuli. 5/n
There was a difference: neurons became less spiky, and after 4 h of short "flashes" they hated long inputs, and didn't respond to them at all. After longer "looms" they still responded to longer stimuli: weaker than in control, but still responded. 6/n
(Now, it is tempting to assume that looming stimuli were just weaker than flashes. The thing is that from my 2014 paper we know that looming stimuli cause stronger activation in the tectum, so it's really not about the amount of activation; it's about its timing) 7/n
So, not only tectal neurons are temporally tuned, but they can retune after sensory stimulation. What about MULTISENSORY stimulation? Would sound retune them as well? We tried some clicks, and also combined clicks with flashes. There were changes! 8/n
Sound clicks alone tuned neurons similar to visual stimuli: they made them less spiky. If however we added sound to visual stimuli (either in-, or out of sync), sound NEGATED the effect of visual stimuli. Maybe it's inhibition in the tectum, or maybe it's something fancier! 9/n
And finally, we probed synaptic inputs to each neuron, and compared their duration to cell's intrinsic temporal tuning. We found that neurons that experience long synaptic currents actually prefer short inputs, and vice versa. The effect is weak, but significant. 10/n
But then of course 4h of sensory stimulation messes up with this effect, and any trace of fine within-network tuning disappears. After a brutal disco party, neurons only respond to short stimuli, and also receive shorter stimuli (prob. because recurrent activity gets shorter) n/n
That’s it. And also, when I said “new preprint from my lab”, it was a bit of role-playing, as it is actually the FIRST preprint from my lab, and in fact the first fully independent paper from my lab, ever. It’s just a bit awkward to admit that it took us 4 years to finish it =)
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