Experience Essential in the Development of Specific Brain Circuit Dynamics

How important is sensory experience in the detailed setup of brain circuits during development? The nature versus nurture debate is no longer an either/or question but is a matter of when and how genetic, molecular, and environmental factors interact and affect each other during the development of the brain.

The recent paper “Emergence of cortical inhibition by coordinated sensory-driven plasticity at distinct synaptic loci” published October 2010 in Nature Neuroscience reports on research investigating if sensory experience is required to set up a specific layer 4 neural circuit in the whisker associated cerebral cortex (barrel cortex) for the circuit to display the sensory processing characteristics observed in the adult.

The circuit the research team was concerned with consisted of three types of neurons. The primary thalamic input neuron, which is excitatory and synapses in layer 4 on both excitatory spiny stellate cells and inhibitory interneurons.

Spiny stellate cells display feed forward inhibition. Layer 4 inhibitory interneurons receive direct excitatory thalamic input that prompts them to send inhibitory signals forward to spiny stellate cells (feed forward inhibition). The inhibitory signal reaches the spiny stellate cells a short time after they receive the same direct excitatory thalamic cell input that the interneurons received.

The team found that, in mice, normal experience using their whiskers (technically vibrissae) was essential for the development of the short thalamic input response in layer 4 spiny stellate cells of the barrel cortex. Each of two independent mechanisms that contributed to the characteristic response required sensory experience to develop. One was strengthening excitatory thalamic cell input onto layer 4 inhibitory interneurons. This occurred by increasing the probability of neurotransmitter release at synapses on the interneurons. The other was an experience dependent decrease in the amount of NMDA receptor activity at excitatory thalamic cell input onto layer 4 spiny stellate cells. The combination of these two mechanisms results in the characteristic short integration time window seen in the layer 4 spiny stellate cells.

Other related blog posts:

Wiggling Whiskers for a Living?

Wiggling Whiskers: Directional Tuning

Whisker Related Brain Anatomy Data for Building Simulations

Wiggling Whiskers: Neurons in the Barrel Cortex and Object Localization

Adult Brain is Continually Modified by Experience: Demonstration in the Whisker System

The Connectome: Video Journey Through Brain Microcircuitry