Cholinergic inputs from Basal forebrain add an excitatory bias to odor coding in the olfactory bulb

Area of Science:

• Neuroscience
• Sensory Processing
• Cholinergic Systems

Background:

• Cholinergic modulation influences attention and learning, but its precise neural circuits and temporal dynamics in sensory processing are unclear.
• Widespread cholinergic projections complicate understanding their specific effects on interconnected brain structures.

Purpose of the Study:

• To investigate how basal forebrain cholinergic projections modulate olfactory bulb (OB) output in mice.
• To elucidate the temporal dynamics and mechanisms of cholinergic influence on the initial stage of olfactory processing.

Main Methods:

• Optogenetic activation of basal forebrain cholinergic axons directly within the OB.
• Recording of mitral/tufted cell spiking activity in response to cholinergic stimulation and olfactory input.
• Analysis of cholinergic signaling dependence and comparison with direct basal forebrain neuron activation.

Main Results:

• Cholinergic stimulation increased mitral/tufted cell spike output, even without sensory input.
• Modulation was rapid, transient, and dependent on local OB cholinergic signaling.
• Cholinergic enhancement of odorant responses was robust, adding an excitatory bias rather than increasing gain or sharpening responses.

Conclusions:

• Basal forebrain cholinergic projections dynamically regulate OB output by exciting mitral/tufted cells.
• This cholinergic mechanism likely enhances odor sensitivity or salience during active olfactory sensing.