Sperry versus Hebb: topographic mapping in Isl2/EphA3 mutant mice

Area of Science:

• Neuroscience
• Computational Neuroscience
• Developmental Neuroscience

Background:

• Retinal ganglion cell axons project topographically to the superior colliculus in wild-type mice.
• This precise projection relies on molecular labels (Eph receptors/ephrins) and correlated neural activity.
• Mutations affecting these factors, like in Isl2/EphA3 mice, disrupt topographic order.

Purpose of the Study:

• To investigate a computational model of retinocollicular connectivity formation.
• To determine how molecular labels and correlated neural activity interact.
• To explain the partial restoration of topographic projection in specific mutant mice.

Main Methods:

• Developed a computational model integrating molecular labels and correlated neural activity.
• Analyzed the model's predictions for retinocollicular mapping.
• Interpreted experimental results from Isl2/EphA3 mutant mice in light of the model.

Main Results:

• Correlated neural activity, via Hebbian learning, can restore topographic connectivity despite conflicting molecular cues.
• This restoration occurs because neural activity carries independent positional information.
• The model explains observations in Isl2/EphA3 heterozygous and knockin/knockout mice, including reduced label levels.

Conclusions:

• Experiments in Isl2/EphA3 mice probe the interplay between molecular labels and correlated activity in neural development.
• Correlated neural activity demonstrates a capacity to partially restore topographic order, even with conflicting molecular signals.