K. Ulrich Bayer, Éric LeBel, Greg L. McDonald, Heather O'Leary, Howard Schulman, and Paul De Koninck
Ca2+/calmodulin (CaM)-dependent kinase (CaMKII) and the NMDA receptor subunit NR2B are established contributors to synaptic plasticity. This week, Bayer et al. show that the activity- and NMDA-receptor-dependent translocation of CaMKII to the synapse has two phases. Using site-directed mutagenesis, the authors document a two-phase binding scheme whereby transient activity elicited Ca2+/ CaM-dependent binding of NR2B to CaMKII at its substrate-binding site ("S-site"), whereas prolonged activity led to persistent binding at the T286-binding site ("T-site"). This interaction prevented binding of the regulatory region, thus creating a second mechanism that allows sustained CaMKII activity and compartmentalization at synapses. Although Ca2+/ CaM was not required for the T-site binding, it may speed the transition.
2. Modeling Perceptual Decisions
Kong-Fatt Wong and Xiao-Jing Wang
Several groups have examined perceptual decision making in primates using forced-choice visual motion discrimination tasks. On these tasks, firing in the lateral intraparietal cortex (LIP) correlates with the reaction time and the correctness of the choice. This activity builds over several hundred milliseconds, suggesting that LIP could be integrating information before a decision. This week, Wang and Wong built a spiking-neuron network model that was able to mimic these activity patterns. Reverberant excitation mediated by NMDA receptors was critical for the slow time integration. The model also explained the experimentally observed longer reaction time in error trials compared with correct trials.