Figure 3: STDP during circuit reactivation results in LTP.

(a) A small reliable population of neurons responded to the stimulating electrode. Red cells responded at least 80% of the time. Scale bar, 50 μm. (b) Histogram of the probability that any neuron within the imaged field will respond to the applied stimulus from the same experiment in a. Only cells that fired in response to more than one stimulation are included. (c) The average EPSP recorded in a L2/3 pyramidal neuron across all stimulations from the same experiment. Ten minutes of EPSP amplitudes were tested for stability before pairing. (d) The distribution of EPSP amplitude drift after bootstrap reshuffling the residuals to the best linear fit. The red line indicates the slope with no shuffling. (e) Online detection of a circuit reactivation was accomplished using a window discriminator triggered off of the accompanying membrane depolarization in the patched L2/3 cell. After a fixed delay, a circuit pairing was activated. Action potentials are truncated for display purposes. (f) Ca²⁺ imaging reveals that temporal structure of the circuit reactivation is preserved when aligned relative to the time of the circuit pairing (t=0). Raster plots of cells for multiple circuit pairings (left y axis), where colour indicates cell identity, show preservation in the order of firing between neurons. Superimposed are response curves of these same cells (right axis). All responses are aligned to the pairing. (g) Example of a CDP experiment. Baseline individual EPSP amplitudes are illustrated (light blue). Circuit pairings were executed based on online detection of spontaneous circuit reactivations (black arrows) over the time course of 40 min. After circuit pairings, individual EPSP amplitudes are illustrated (dark blue). Inset: the average EPSP amplitude before (n=60, light blue) and after circuit pairing (n=60, dark blue). Input resistance, series resistance and resting membrane potential were all monitored for stability during the testing of EPSPs. The asterisk represents a spontaneous circuit reactivation during the test period, transiently shifting the measures.