Periodic Reporting for period 1 - EpiNeuron (Tracing human cortical neurons involved in epileptic processes at multiple scales)
Okres sprawozdawczy: 2023-09-01 do 2025-08-31
Epilepsy affects more than 50 million people worldwide, and about one-third of patients do not respond to medication. The causes of uncontrolled seizures lie in the abnormal activity of specific neurons, yet the detailed behaviour of these cells in the human brain is still largely unknown. Most available knowledge comes from animal experiments, which differ from human neurophysiology in key aspects such as neuronal size, connectivity, and chemical environment.
The EpiNeuron project aimed to bridge this knowledge gap by directly studying the electrical activity of neurons in patients undergoing pre-surgical assessment for drug-resistant epilepsy. Using microelectrodes implanted during surgery, the project recorded neuronal firing at high temporal resolution and compared these findings with data obtained from the same patients’ brain tissue after surgery. The ultimate goal was to identify how different types of neurons - particularly excitatory principal cells and inhibitory interneurons - contribute to epileptogenic processes.
By combining in vivo and in vitro approaches, the project sought to determine which neuronal properties are intrinsic and which depend on the surrounding network. This knowledge is essential for understanding epileptogenic mechanisms and, in the longer term, for developing more targeted therapeutic strategies.
The EpiNeuron project aimed to bridge this knowledge gap by directly studying the electrical activity of neurons in patients undergoing pre-surgical assessment for drug-resistant epilepsy. Using microelectrodes implanted during surgery, the project recorded neuronal firing at high temporal resolution and compared these findings with data obtained from the same patients’ brain tissue after surgery. The ultimate goal was to identify how different types of neurons - particularly excitatory principal cells and inhibitory interneurons - contribute to epileptogenic processes.
By combining in vivo and in vitro approaches, the project sought to determine which neuronal properties are intrinsic and which depend on the surrounding network. This knowledge is essential for understanding epileptogenic mechanisms and, in the longer term, for developing more targeted therapeutic strategies.
During the two-year fellowship, the project investigated how individual neurons behave in the human brain during epilepsy, combining unique in vivo and in vitro approaches.
Neuronal activity was analysed from 26 patients undergoing pre-surgical evaluation for drug-resistant epilepsy, using hybrid clinical–research electrodes capable of detecting both large-scale brain signals and the tiny voltage changes produced by single neurons. In addition, recordings were obtained from 27 postoperative brain tissue samples, where neurons could be studied under controlled laboratory conditions using high-density microelectrode arrays.
The in vivo part of the project exceeded expectations. From these recordings, the electrical activity of over one thousand individual neurons was successfully isolated and classified into two main categories—principal cells and interneurons—based on the shape and duration of their action potentials. This large-scale dataset provided one of the most detailed views to date of human neuronal behaviour in epileptic brain tissue.
A key outcome of the project was the development of a new computational algorithm to identify and analyse burst firing—short, rapid sequences of electrical impulses that indicate intense neuronal activation. Using this method, the study provided one of the first systematic descriptions of bursting behaviour in human single-unit recordings. The results revealed that not only excitatory principal cells but also inhibitory interneurons are capable of generating bursts, challenging earlier assumptions and suggesting that bursting is a more universal feature of human neuronal communication than previously thought.
The in vitro recordings complemented these results by offering a controlled environment to explore intrinsic neuronal excitability. Comparative analyses between the two datasets showed that, when isolated from their natural network, interneurons fired less frequently, while principal cells retained similar levels of spontaneous activity. This indicates that interneurons are more dependent on network input, whereas principal cells maintain self-driven firing even in isolation.
Importantly, the same waveform-based classification criteria applied to both datasets produced consistent results, confirming the robustness and reproducibility of the analytical framework.
Finally, an additional measure of firing variability, the short-timescale irregularity coefficient (CV2), revealed that neurons in vitro fired more regularly than those in vivo. This suggests that the natural synaptic environment of the human brain introduces additional variability—an expected signature of ongoing network activity.
Neuronal activity was analysed from 26 patients undergoing pre-surgical evaluation for drug-resistant epilepsy, using hybrid clinical–research electrodes capable of detecting both large-scale brain signals and the tiny voltage changes produced by single neurons. In addition, recordings were obtained from 27 postoperative brain tissue samples, where neurons could be studied under controlled laboratory conditions using high-density microelectrode arrays.
The in vivo part of the project exceeded expectations. From these recordings, the electrical activity of over one thousand individual neurons was successfully isolated and classified into two main categories—principal cells and interneurons—based on the shape and duration of their action potentials. This large-scale dataset provided one of the most detailed views to date of human neuronal behaviour in epileptic brain tissue.
A key outcome of the project was the development of a new computational algorithm to identify and analyse burst firing—short, rapid sequences of electrical impulses that indicate intense neuronal activation. Using this method, the study provided one of the first systematic descriptions of bursting behaviour in human single-unit recordings. The results revealed that not only excitatory principal cells but also inhibitory interneurons are capable of generating bursts, challenging earlier assumptions and suggesting that bursting is a more universal feature of human neuronal communication than previously thought.
The in vitro recordings complemented these results by offering a controlled environment to explore intrinsic neuronal excitability. Comparative analyses between the two datasets showed that, when isolated from their natural network, interneurons fired less frequently, while principal cells retained similar levels of spontaneous activity. This indicates that interneurons are more dependent on network input, whereas principal cells maintain self-driven firing even in isolation.
Importantly, the same waveform-based classification criteria applied to both datasets produced consistent results, confirming the robustness and reproducibility of the analytical framework.
Finally, an additional measure of firing variability, the short-timescale irregularity coefficient (CV2), revealed that neurons in vitro fired more regularly than those in vivo. This suggests that the natural synaptic environment of the human brain introduces additional variability—an expected signature of ongoing network activity.
The EpiNeuron project advanced our understanding of human neuronal function in epilepsy well beyond the current state of the art. While most previous knowledge about neuronal firing patterns has come from animal models, this project provided one of the first large-scale quantitative analyses of single-cell activity directly recorded in the human brain. By integrating in vivo recordings from patients and in vitro measurements from their postoperative brain tissue, the project bridged two experimental worlds that are rarely combined in neuroscience.
A major methodological innovation was the development of a new burst-detection algorithm tailored to human in vivo data. This algorithm allowed precise identification of short, high-frequency firing episodes that reflect sudden increases in neuronal excitability. The method can also be adapted to other recording conditions - both in vitro and in animal models - making it a broadly applicable tool for studying how neurons encode information or become dysregulated during disease.
Beyond the methodological advance, the findings challenge long-standing assumptions about human neuronal behaviour. Traditionally, burst firing was thought to be limited to excitatory neurons, but the project demonstrated that inhibitory interneurons also display this activity pattern. This discovery suggests that bursting is not confined to a single cell class but represents a fundamental communication mode of the human brain.
In practical terms, this work lays the foundation for identifying cell-type-specific markers of epileptogenic zones. In the longer term, such markers could aid in the prediction of seizure onset or in the design of therapies that selectively target hyperactive neuronal populations. The project therefore contributes not only to basic neuroscience but also to translational research with potential clinical relevance.
A major methodological innovation was the development of a new burst-detection algorithm tailored to human in vivo data. This algorithm allowed precise identification of short, high-frequency firing episodes that reflect sudden increases in neuronal excitability. The method can also be adapted to other recording conditions - both in vitro and in animal models - making it a broadly applicable tool for studying how neurons encode information or become dysregulated during disease.
Beyond the methodological advance, the findings challenge long-standing assumptions about human neuronal behaviour. Traditionally, burst firing was thought to be limited to excitatory neurons, but the project demonstrated that inhibitory interneurons also display this activity pattern. This discovery suggests that bursting is not confined to a single cell class but represents a fundamental communication mode of the human brain.
In practical terms, this work lays the foundation for identifying cell-type-specific markers of epileptogenic zones. In the longer term, such markers could aid in the prediction of seizure onset or in the design of therapies that selectively target hyperactive neuronal populations. The project therefore contributes not only to basic neuroscience but also to translational research with potential clinical relevance.