Spontaneous activity in the piriform cortex extends the dynamic range of cortical odor coding.

Area of Science:

• Neuroscience
• Olfactory System Research
• Sensory Processing

Background:

• Neurons in the neocortex show spontaneous activity, but its source and purpose are unclear.
• Spontaneous spiking is also observed in the primary olfactory (piriform) cortex, a sensory paleocortex in mice.

Purpose of the Study:

• To investigate the origin and function of spontaneous neural activity in the piriform cortex.
• To determine how spontaneous activity influences odor representation and coding.

Main Methods:

• Electrophysiological recordings from piriform cortex neurons in mice.
• Analysis of spontaneous firing rates and responses to odor stimulation.
• Investigation of the role of NMDA receptors and olfactory bulb input.

Main Results:

• Piriform neurons exhibit spontaneous firing with rates varying by neuronal class.
• This activity depends on NMDA receptors and originates from the olfactory bulb.
• Odor stimulation elicits excitation in ~15% of neurons and suppression in ~15%, revealing bidirectional responses.
• Neuronal responsiveness is less sparse than previously thought due to bidirectional changes.

Conclusions:

• Spontaneous activity in the piriform cortex is driven by bottom-up input and modulated by NMDA receptors.
• Bidirectional spiking (excitation and suppression) around an elevated baseline expands the dynamic range of odor representation.
• Spontaneous activity enriches the neural coding space for complex olfactory stimuli, improving odor perception.