Development and spike timing-dependent plasticity of recurrent excitation in the Xenopus optic tectum.

Much of the information processing in the brain occurs at the level of local circuits; however, the mechanisms underlying their initial development are poorly understood. We sought to examine the early development and plasticity of local excitatory circuits in the optic tectum of Xenopus laevis tadpoles. We found that retinal input recruits persistent, recurrent intratectal synaptic excitation that becomes more temporally compact and less variable over development, thus increasing the temporal coherence and precision of tectal cell spiking. We also saw that patterned retinal input can sculpt recurrent activity according to a spike timing-dependent plasticity rule, and that impairing this plasticity during development results in abnormal refinement of the temporal characteristics of recurrent circuits. This plasticity is a previously unknown mechanism by which patterned retinal activity allows intratectal circuitry to self-organize, optimizing the temporal response properties of the tectal network, and provides a substrate for rapid modulation of tectal neuron receptive-field properties.