Theory of optimal balance predicts and explains the amplitude and decay time of synaptic inhibition

Recovery of consolidation after sleep following stroke-interaction of slow waves, spindles, and GABA

Sleep is known to promote recovery after stroke. Yet it remains unclear how stroke affects neural processing during sleep. Using an experimental stroke model in rats along with electrophysiological monitoring of neural firing and sleep microarchitecture, here we show that sleep processing is altered by stroke. We find that the precise coupling of spindles to global slow oscillations (SOs), a phenomenon that is known to be important for memory consolidation, is disrupted by a pathological increase in "isolated" local delta waves. The transition from this pathological to a physiological state-with increased spindle coupling to SO-is associated with sustained performance gains during recovery. Interestingly, post-injury sleep could be pushed toward a physiological state via a pharmacological reduction of tonic γ-aminobutyric acid (GABA). Together, our results suggest that sleep processing after stroke is impaired due to an increase in delta waves and that its restoration can be important for recovery.

The Objective Bayesian Probability that an Unknown Positive Real Variable Is Greater Than a Known Is 1/2

If there are two dependent positive real variables x1 and x2, and only x1 is known, what is the probability that x2 is larger versus smaller than x1? There is no uniquely correct answer according to “frequentist” and “subjective Bayesian” definitions of probability. Here we derive the answer given the “objective Bayesian” definition developed by Jeffreys, Cox, and Jaynes. We declare the standard distance metric in one dimension, d(A,B)≡|A−B|, and the uniform prior distribution, as axioms. If neither variable is known, P(x2<x1)=P(x2>x1). This appears obvious, since the state spaces x2<x1 and x2>x1 have equal size. However, if x1 is known and x2 unknown, there are infinitely more numbers in the space x2>x1 than x2<x1. Despite this asymmetry, we prove P(x2<x1∣x1)=P(x2>x1∣x1), so that x1 is the median of p(x2|x1), and x1 is statistically independent of ratio x2/x1. We present three proofs that apply to all members of a set of distributions. Each member is distinguished by the form of dependence between variables implicit within a statistical model (gamma, Gaussian, etc.), but all exhibit two symmetries in the joint distribution p(x1,x2) that are required in the absence of prior information: exchangeability of variables, and non-informative priors over the marginal distributions p(x1) and p(x2). We relate our conclusion to physical models of prediction and intelligence, where the known ’sample’ could be the present internal energy within a sensor, and the unknown the energy in its external sensory cause or future motor effect.

Corelease of Inhibitory Neurotransmitters in the Mouse Auditory Midbrain

The central nucleus of the inferior colliculus (ICC) of the auditory midbrain, which integrates most ascending auditory information from lower brainstem regions, receives prominent long-range inhibitory input from the ventral nucleus of the lateral lemniscus (VNLL), a region thought to be important for temporal pattern discrimination. Histological evidence suggests that neurons in the VNLL release both glycine and GABA in the ICC, but functional evidence for their corelease is lacking. We took advantage of the GlyT2-Cre mouse line (both male and female) to target expression of ChR2 to glycinergic afferents in the ICC and made whole-cell recordings in vitro while exciting glycinergic fibers with light. Using this approach, it was clear that a significant fraction of glycinergic boutons corelease GABA in the ICC. Viral injections were used to target ChR2 expression specifically to glycinergic fibers ascending from the VNLL, allowing for activation of fibers from a single source of ascending input in a way that has not been previously possible in the ICC. We then investigated aspects of the glycinergic versus GABAergic current components to probe functional consequences of corelease. Surprisingly, the time course and short-term plasticity of synaptic signaling were nearly identical for the two transmitters. We therefore conclude that the two neurotransmitters may be functionally interchangeable and that multiple receptor subtypes subserving inhibition may offer diverse mechanisms for maintaining inhibitory homeostasis.SIGNIFICANCE STATEMENT Corelease of neurotransmitters is a common feature of the brain. GABA and glycine corelease is particularly common in the spinal cord and brainstem, but its presence in the midbrain is unknown. We show corelease of GABA and glycine for the first time in the central nucleus of the inferior colliculus of the auditory midbrain. Glycine and GABA are both inhibitory neurotransmitters involved in fast synaptic transmission, so we explored differences between the currents to establish a physiological foundation for functional differences in vivo In contrast to the auditory brainstem, coreleased GABAergic and glycinergic currents in the midbrain are strikingly similar. This apparent redundancy may ensure homeostasis if one neurotransmitter system is compromised.