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[0] Froemke RC, Merzenich MM, Schreiner CE, A synaptic memory trace for cortical receptive field plasticity.Nature 450:7168, 425-9 (2007 Nov 15)

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ref: -2010 tags: neural signaling rate code patch clamp barrel cortex date: 03-18-2021 18:41 gmt revision:0 [head]

PMID-20596024 Sensitivity to perturbations in vivo implies high noise and suggests rate coding in cortex

  • How did I not know of this paper before.
  • Solid study showing that, while a single spike can elicit 28 spikes in post-synaptic neurons, the associated level of noise is indistinguishable from intrinsic noise.
  • Hence the cortex should communicate / compute in rate codes or large synchronized burst firing.
    • They found large bursts to be infrequent, timing precision to be low, hence rate codes.
    • Of course other examples, e.g auditory cortex, exist.

Cortical reliability amid noise and chaos

  • Noise is primarily of synaptic origin. (Dropout)
  • Recurrent cortical connectivity supports sensitivity to precise timing of thalamocortical inputs.

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ref: Froemke-2007.11 tags: nucleus basalis basal forebrain acetylcholine auditory cortex potentiation voltage clamp date: 10-08-2008 22:44 gmt revision:2 [1] [0] [head]

PMID-18004384[0] A synaptic memory trace for cortical receptive field plasticity.

  • nucleus basalis = basal forebrain!
  • stimulation of the nucleus basalis caused a reorganization of the auditory cortex tuning curves hours after the few minutes of training.
  • used whole-cell current-clamp recording to reveal tone-evoked excitatory and inhibitory postsynaptyic currents.
  • pairing of nucleus basalis and auditory tone presentation (2-5 minutes) increased excitatory currents and decreased inhibitory currents as compared to other (control) frequencies.
  • tuning changes required simultaneous tone presentation and nucleus basalis stimulation. (Could they indiscriminately stimulate the NB? did they have to target a certain region of it? Seems like it.)
    • did not require postsynaptic spiking!
  • Pairing caused a dramatic (>7-fold) increase in the probability of firing bursts of 2+ spikes
  • Cortical application of atropine, an acetylcholine receptor antagonist, prevented the effects of nucleus basalis pairing.
  • the net effects of nucleus basalis pairing are suppression of inhibition (20 sec) followed by enhancement of excitation (60 sec)
  • also tested microstimulation of the thalamus and cortex; NB pairing increased EPSC response from intracortical microstim, but not from thalamic stimulation. Both cortical and thalamic stimulation elicited an effect in the voltage-clamped recorded neuron.
  • by recording from the same site (but different cells), they showed that while exitation persisted hours after pairing, inhibition gradually increased commensurate with the excitation.
  • Thus, NB stimulation leaves a tag of reduced inhibition (at the circuit level!), specifically for neurons that are active at the time of pairing.

____References____

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ref: Cooper-2000.09 tags: globus pallidus electrophysiology current clamp channel date: 0-0-2007 0:0 revision:0 [head]

PMID-10970430 Electrophysiological and morphological characteristics of three subtypes of rat globus pallidus neurone in vitro

  • there are 3 morphological types of neurons.
    • A: inward rectfier + low-threshold calcium current = anode break depolarizations.
    • B: no inward rectifier, just fast monophasic AHP. small.
    • C: big! (...)