Gain Modulation of Synaptic Inputs by Network State in Auditory Cortex In Vivo

RAMON REIG ; YANN ZERLAUT; RAMIRO VERGARA; ALAIN DESTEXHE; MARIA V. SANCHEZ-VIVES

JOURNAL OF NEUROSCIENCE

SOC NEUROSCIENCE

Lugar: Washington; Año: 2015 vol. 35 p. 2689 - 2702

0270-6474

The cortical network recurrent circuitry generates spontaneous activity organized into Up (active) and Down (quiescent) states duringslow-wave sleep or anesthesia. These different states of cortical activation gain modulate synaptic transmission. However, the reportedmodulation that Up states impose on synaptic inputs is disparate in the literature, including both increases and decreases of responsive-ness. Here, we tested the hypothesis that such disparate observations may depend on the intensity of the stimulation. By means ofintracellular recordings, we studied synaptic transmission during Up and Down states in rat auditory cortex in vivo. Synaptic potentialswere evoked either by auditory or electrical (thalamocortical, intracortical) stimulation while randomly varying the intensity of thestimulus. Synaptic potentials evoked by the same stimulus intensity were compared in Up/Down states. Up states had a scaling effect onthe stimulus-evoked synaptic responses: the amplitude of weaker responses was potentiated whereas that of larger responses wasmaintained or decreased with respect to the amplitude during Down states. We used a computational model to explore the potentialmechanisms explaining this nontrivial stimulus?response relationship. During Up/Down states, there is different excitability in thenetwork and the neuronal conductance varies. We demonstrate that the competition between presynaptic recruitment and the changingconductance might be the central mechanism explaining the experimentally observed stimulus?response relationships. We concludethat the effect that cortical network activation has on synaptic transmission is not constant but contingent on the strength of thestimulation, with a larger modulation for stimuli involving both thalamic and cortical networks.