Self-regulation and Electrically Evoked Precisely Timed Cortical Culture Activity As a Means to Control a Hybrot
35th Annual Meeting of the Society for Neuroscience, Washington, DC, 2005. Prog. no. 276.19
Our lab embodies cultured cortical networks in an artificial environment to investigate how associations are formed by the network based on its environmental interactions. This requires creating a sensory feedback stimulation that induces neural plasticity and finding a reliable measure of network state to inform motor commands. Neurons modify their activity through synaptic and intrinsic plasticity mechanisms and temper these changes through homeostatic mechanisms. Here, we alter network activity by adding constant frequency stimulation termed context, a type of “artificial plasticity”, and study the subsequent self-regulatory behavior. A neural response after stimulation is due to a combination of the electrically evoked and ongoing neural activity. By measuring responses to a repeated stimulation termed probe, changes are due solely to changes in network state; the instantaneous stimulation rate was low to avoid transmitter depletion and stimulation during network refractory periods. Early evoked activity from an extra-cellular electrode are precisely timed (jitter less than 1 ms) and detected on multiple electrodes up to 15 ms after the stimulation of a Multi-Electrode Array. These precisely-timed spikes are pre-synaptic as they occur when synaptic activity is blocked (CNQX, APV, Bicuculline). Their latencies changed during and between various paired sets of context and probe stimulations, suggesting plasticity occurred in intrinsic cell excitability and/or in synaptic strengths between the first evoked activity and later precisely-timed activity. The same stimulation done in the presence of blockers did not produce latency changes, suggesting they were synaptic in origin. Thus, this spatio-temporal spike structure is a measure of network state. For the control of a hybrot using an embodied neural network, the context stimulations scale to represent various sensory feedback, and precisely-timed spikes map to motor commands.