Synaptic Plasticity in the Somatosensory Cortex

The term synaptic plasticity implies modification in the strength or efficacy of synaptic transmission between pre-existing synapses. Long-term changes in synaptic efficacy have been widely proposed as the cellular mechanism of the learning and memory machineries of the brain. However both the induction and expression mechanisms of synaptic plasticity processes remain elusive and more diverse than formerly though. In this review we show the principal mechanisms of experience-dependent plasticity in the somatosensory barrel cortex. The somatosensory barrel cortex is composed of local circuits interconnected by vertical and horizontal projections. Sensory information from the whiskers is transmitted through the brain stem and thalamus to layer 4 neurons in the barrel cortex. Sensory responses are relayed from layer 4 to layer 2/3 and then to layer 5 and layer 6. At the same time, there is feedback from layer 5 to layer 2/3 and layer 6 to layer 4. This vertical organization is linked horizontally by strong projections between barrels. Distinct synaptic and intrinsic properties of these neurons are involved in different sensory plasticity responses observed in the barrel cortex.