Gain modulation of synaptic inputs by network state in auditory cortex in vivo

Area of Science:

• Neuroscience
• Computational Neuroscience

Background:

• Cortical networks exhibit spontaneous Up and Down states during sleep and anesthesia.
• These states influence synaptic transmission, but reported effects on responsiveness are inconsistent.

Purpose of the Study:

• To investigate if stimulus intensity explains disparate findings on Up state modulation of synaptic transmission.
• To elucidate the mechanisms underlying the stimulus-dependent modulation of synaptic responses.

Main Methods:

• Intracellular recordings in rat auditory cortex in vivo.
• Evoked synaptic potentials via auditory and electrical (thalamocortical, intracortical) stimulation.
• Varying stimulus intensity and comparing responses during Up and Down states.
• Computational modeling to explore underlying mechanisms.

Main Results:

• Up states exhibit a scaling effect on stimulus-evoked synaptic responses.
• Weak responses were potentiated, while strong responses were maintained or decreased during Up states compared to Down states.
• A computational model identified competition between presynaptic recruitment and changing neuronal conductance as a key mechanism.

Conclusions:

• The impact of cortical Up states on synaptic transmission is stimulus-dependent.
• This dependency is explained by the interplay of neuronal excitability, conductance changes, and presynaptic recruitment.
• Stimuli engaging both thalamic and cortical networks show greater modulation.