PhD Scientific Days 2024

Poster Session D - Neurosciences 1.

Bridging in vivo and in vitro recordings in the human epileptic neocortex: patient-wise comparative analysis of single-unit activities

Text of the abstract

Introduction: Epilepsy provides a unique opportunity to study human cellular electrophysiology through in vivo and in vitro approaches. In vivo recordings offer advantages in action potential pattern reconstruction and connection preservation, while in vitro studies allow broader tissue exploration within a confined space of cut connections, yet coherent investigation in these distinct conditions is lacking.
Aims & Method: This study compared single-neuron firing properties in four epileptic patients using identical 24-channel laminar microelectrodes with 150 μm inter-contact distance for both their in vivo and in vitro intracortical recordings. Automated spike sorting algorithms were employed for single-unit analysis, based on which unit waveforms, correlograms, firing rates, burstiness index, and determination of excitatory and inhibitory features were calculated.
Results: Identifying 330 single neurons in vitro and 22 in vivo, we observed a significantly higher overall firing rate for in vitro (2.738 Hz) than in vivo cells (1.321 Hz, p<0.0001). The firing rate of principal cells was not different (2.71 Hz in vitro vs. 2.73 Hz in vivo), while interneurons discharged with a higher rate in vitro, than in vivo (2.93 vs. 0.74 Hz). The burstiness of all cells was significantly higher in vivo (6.986%) than in vitro (3.506%, p=0.0006). Patient-wise in vivo and in vitro unit numbers correlated strongly (r=0.703). Layer-specific analysis revealed high correlations (0.926 for firing rates, 0.762 for burstiness indices).
Discussion: Disparities in firing rates and burstiness highlight the differences between in vivo and in vitro conditions. In vitro neurons, especially inhibitory cells with limited synaptic connections show higher activity than those in the intact neocortex. The lower burstiness in vitro might also be linked to the partial loss of synaptic inputs, but the different environment provided by the bathing solution might also account for the observed differences.
Funding:
National Research, Development and Innovation Office K137886 and Bolyai Fellowship
Hungarian Brain Research Program NAP2022-I-8/2022,
European Union and Hungarian Government: PharmaLab RRF-2.3.1-21-2022-00015
Semmelweis 250+ Scholarship for Excellence
New National Excellence Programme: ÚNKP-23-3