SPATIOTEMPORAL ANALYSIS OF SIMULTANEOUS SINGLE-UNIT ACTIVITY IN THE DRAGONFLY .2. NETWORK CONNECTIVITY

The present work describes a new technique for the identification of "functional connectivity" between neural firing patterns. The simultaneous single-unit recordings obtained from over 50 individual cells in the dragonfly mesothoracic ganglion during three consecutive behavioral states: pre-flight, flight and post-flight were evaluated. Each individual spike train was converted into a synthesized "analog gradient" designed to capture crucial physiological characteristics of the cell from which the spike train emanated. Estimates of network "functional connectivity" were calculated using correlations between analog gradient spike trains for all possible cell pairings. Both functional excitation and inhibition could be detected in the correlations. The detection of functional connectivity was relatively independent of cell firing rate. More detailed analyses indicated the existence of cellular firing histories and connectivity patterns during flight that strongly resembled the characteristics of a bi-stable oscillator. Such an oscillator, hypothetically, could drive the elevator and depressor motor neuron firing patterns that support wing kinematics. There was no evidence for the functional existence of such an oscillator within either pre- or post-flight spike records. The detected spatiotemporal patterns of neural activity are hypothesized to bc consistent with neural command sequences that the dragonfly might use to control flight. The demonstrated capability to define short-time scale functional relationships between spike trains obtained from dragonfly ganglia should have valuable applications to the comparative study of neural information processing strategies in a variety of other neural systems.