Training the developing nervous system
To date, most research on nervous system plasticity has used sensory stimulation and measurements of the induced neural responses. The 'Experience-dependent modifications of developing neural circuits and animal behaviours' (ZEBRAFISH PLASTICITY) project used sensory perception to better isolate neuronal activities. Project researchers used a technique resembling the motion after-effect (MAE). A phenomenon seen in mammals and some insects, continuous coherent motion eventually induces the perception of movement in the opposite direction even after terminating the stimulus. The team opted for the small zebrafish larva to monitor large neural networks as it has conveniently transparent skin. ZEBRAFISH PLASTICITY designed a two-photon microscope to visualise brain activity using fluorescence at a single cell level with a specially developed transgenic line of zebrafish. Results suggest that within the optic tectum exist direction-selective neural networks that correlate with either visual detection or visual perception. Unlike the first group, the visual perception group showed synchronous activities in the absence of visual stimulation with suppressed activity during the conditioning moving stimulus. Imbalance is generated when the first group is habituated to motion perception while the second group is not, resulting in motion illusion. Overall, motion perception requires a specific group and not all direction-selective neurons. As these are randomly distributed within the network, sensory perception seems to depend on activation of a minimum number of direction-selective neurons to induce motion perception. Applications may extend to humans as observations in autistic patients report an enhanced MAE. Accordingly the team has generated a zebrafish with a specially modified gene linked to autism and Rett's syndrome. Future research plans for the team include tests on the new line to elucidate neural circuit anomalies that may lead to autism.
