Cell type specific tracing of the subcortical input to primary visual cortex from the basal forebrain

Area of Science:

• Neuroscience
• Visual System
• Neuroanatomy

Background:

• The basal forebrain (BF) modulates visual function via cholinergic inputs to the primary visual cortex (V1).
• BF afferents target deep V1 layers, with acetylcholine also reaching superficial layers via volume transmission.
• Direct synaptic connections in deep layers could offer immediate V1 modulation.

Purpose of the Study:

• To investigate direct synaptic inputs from the basal forebrain (BF) onto neurons in the primary visual cortex (V1).
• To compare BF inputs with geniculocortical inputs to V1 excitatory and inhibitory neurons.

Main Methods:

• Utilized helper viruses for cell type-specific retrograde infection of pseudotyped and genetically modified rabies virus.
• Targeted infection to trace direct synaptic connections from the BF to V1.

Main Results:

• Found direct synaptic input from the BF onto V1 inhibitory neurons, comparable in number to geniculocortical inputs.
• Identified geniculocortical inputs to V1 excitatory neurons.
• Observed no direct synaptic input from the BF to V1 excitatory neurons.

Conclusions:

• The basal forebrain exerts a direct and immediate influence on local inhibition within the primary visual cortex.
• This direct pathway suggests a distinct mechanism for BF modulation of visual processing, primarily impacting inhibitory circuits.