Interdigitated paralemniscal and lemniscal pathways in the mouse barrel cortex

Area of Science:

• Neuroscience
• Sensory processing
• Cortical circuitry

Background:

• Primary sensory cortical areas receive input through multiple thalamic channels.
• The rodent whisker system utilizes lemniscal and paralemniscal thalamocortical projections from the ventral posteromedial nucleus (VPM) and posterior medial nucleus (POm) respectively.
• The integration of these distinct sensory streams within the neocortical microcircuit remains poorly understood.

Purpose of the Study:

• To investigate the organization of functional thalamocortical and ascending intracortical projections in the mouse barrel cortex.
• To elucidate how lemniscal and paralemniscal pathways are segregated and integrated within the neocortical microcircuit.

Main Methods:

• Quantitative laser scanning photostimulation was employed.
• Neocortical excitatory neurons were recorded while stimulating VPM or POm to map thalamocortical projections.
• Ascending intracortical projections from lemniscal and paralemniscal pathways to layers 2/3 were also mapped.

Main Results:

• Neurons in layers 4, 5, and 6A received dense thalamic input (VPM to L4, L5B, L6A; POm to L5A).
• Layer 2/3 neurons rarely received direct thalamic input.
• Lemniscal inputs from L4 targeted L3 within a column, while paralemniscal inputs from L5A targeted a distinct L2 layer.
• L2 neurons received integrated input from both lemniscal L3 and paralemniscal L5A cells across columns.

Conclusions:

• Lemniscal and paralemniscal information streams are segregated into distinct, interdigitated cortical layers.
• This segregation defines functionally specialized circuits within the barrel cortex for processing whisker sensory information.