BURSTING NEURONAL ACTIVITY IN VIVO: INSIGHTS FROM PRE-SURGICAL MICROELECTRODE RECORDINGS IN PATIENTS WITH DRUG-RESISTANT EPILEPSY

The project aims to analyse neural activity in mesial temporal structures recorded with microelectrodes during intracranial monitoring in patients with drug-resistant epilepsy. Single-unit activity (SUA) can be isolated from long-term recordings, and neurons can be classified as interneurons (IN) or pyramidal cells (PC). Here, we investigated whether bursting neurons can be identified and characterised in vivo in patients with mesial temporal lobe epilepsy.
Intracranial macroelectrodes combined with research microelectrodes were implanted in mesial temporal structures in 25 patients. Local field potentials (LFP), SUA, and multi-unit activity (MUA) were recorded continuously for 2–3 weeks (24/7). Single units were isolated using standard spike-sorting methods during awake periods, and neuronal types were determined from action potential waveform features. Bursting behaviour was then analysed at both the SUA and MUA levels.
We isolated single-unit spikes from MUA, classified neurons as IN or PC, and applied a new burst definition to SUA and MUA. This revealed synchronous bursting across units and may help refine spike sorting. Neurons can be characterised by burstiness, intraburst amplitude dynamics, and interspike intervals (ISI). Burstiness was associated with firing rate and action potential half-width; fast bursting may reduce after-hyperpolarisation (AHP) and relate to higher burst propensity. When bursting was present, interneurons exhibited a greater number of bursts than pyramidal cells. Bursting properties also depended strongly on anatomical location and on whether recordings were obtained within the epileptogenic zone.
Overall, these findings suggest that bursting neurons can be identified and characterised in vivo in patients with mesial temporal lobe epilepsy.