Plasticity in primary somatosensory cortex resulting from environmentally enriched stimulation and sensory discrimination training

Abstract

We studied primary-somatosensory cortical plasticity due to selective stimulation of the sensory periphery by two procedures of active exploration in adult rats. Subjects, left with only three adjacent whiskers, were trained in a roughness discrimination task or maintained in a tactile enriched environment. Either training or enrichment produced 3-fold increases in the barrel cortex areas of behaviorally-engaged whisker representations, in their zones of overlap. While the overall areas of representation expanded dramatically, the domains of exclusive principal whisker responses were virtually identical in enriched vs normal rats and were significantly smaller than either group in roughness discrimination-trained rats. When animals were trained or exposed to enriched environments with the three whiskers arrayed in an arc or row, very equivalent overlaps in representations were recorded across their greatly-enlarged whisker representation zones. This equivalence in distortion in these behavioral preparations is in contradistinction to the normal rat, where overlap is strongly biased only along rows, probably reflecting the establishment of different relations with the neighboring cortical columns. Overall, plasticity phenomena are argued to be consistent with the predictions of competitive Hebbian network plasticity.

Pathway-specific reorganization of projection neurons in somatosensory cortex during learning

“…The increased sensitivity to touch in M1P neurons persisted post-training and could be a result of a strengthening or disinhibition of feedforward responses in S1 (refs. [25][26][27][28][29]. During this period the session-to-session response variability of M1P neurons was reduced compared to baseline conditions, suggesting that sensory representation in these neurons was stabilized.…”

“…Furthermore, they maintained a similar ability to discriminate P100 and P1200 textures across training. Whisker motion representation in M1 has also been found to be reliably encoded at a populationlevel during learning 30 ; thus, sensorimotor integration across S1 and M1 maintains a faithful sensory representation that is stabilized by the recruitment of additional neurons during learning 26,31 . The adoption of active whisking strategies to physically drive relevant kinematics [13][14][15][16] , and possibly an additional modulation of S1 by M1 activity during active whisking 2,32,33 , might serve to improve the fidelity of this representation.…”

Environmental enrichment and the sensory brain: the role of enrichment in remediating brain injury

“…Thus, in the rodent barrel cortex that receives tactile input from the mystacial whiskers, EE caused a decrease in receptive field size and in neuronal responses evoked by stimulation of the “Principal Whisker” (the topographically matched whisker providing the main input to a group of neurons in the barrel cortex) in supragranular cortical Layers 2/3, but there were no changes in response strength or receptive field size in input Layer 4 (Polley et al, 2004). It is worth noting that Guic et al (2008) found that EE caused an increase in cortical representational area in Layer 4. However, these effects were seen after stimulation of only a few selective whiskers, while other whiskers were trimmed whereas Polley et al (2004) used a non-deprived paradigm where all whiskers remained untrimmed.…”

Behaviour-dependent recruitment of long-range projection neurons in somatosensory cortex

“…Although the behaviour strategy used by the animal ('active sensing' versus 'detection amid distractors') 22,24 cannot be distinguished, our activation patterns are in line with previous reports indicating that S1-M1 integration may inform the decision of the mouse under this task condition [18][19][20] . As sensory stimulus features alone are not sufficient to produce these differential activation patterns among S2P and M1P neurons, we speculate that other mechanisms could be involved, including plasticity of local and long-range circuits during task learning 27,28 or topdown influences exerted by feedback circuits or attention-related brain areas during task engagement 29,30 . Understanding the circuits and mechanisms underlying this selective routing of sensory information will warrant further investigation.…”