Abstract
Transcranial focused ultrasound (tFUS) offers unique advantages for neuromodulation, including its non-invasive nature, deep penetration capabilities, and millimeter-scale spatial resolution that enables targeting specific brain regions with precision unattainable by transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS). The cerebellum represents an attractive target for tFUS due to its extensive bidirectional connectivity with numerous cerebral regions, including the hippocampus. While traditionally considered primarily a motor-related brain region, the cerebellum has now been regarded as a key structure in cognitive processing, emotional regulation, and spatial navigation. This cerebellar influence on diverse brain functions occurs through parallel multi-synaptic connections to nuclei such as the hippocampus, where seizures often originate in the temporal lobe, making it an ideal intervention target. Epilepsy affects millions worldwide, with approximately one-third of patients remaining resistant to traditional drug treatments. This creates an urgent need for alternative therapeutic approaches. Traditional neuromodulation approaches for epilepsy management often involve invasive procedures with associated risks, highlighting the need for non-invasive alternatives. Cerebellum-targeted tFUS offers a promising therapeutic strategy by modulating downstream hippocampal and whole-brain neural activity through natural neural pathways, potentially providing effective seizure control without invasive procedures.This thesis addressed these issues in two parts. The first part investigated the effects of cerebellum-targeted tFUS on hippocampal and whole-brain neural activity. The first study established the fundamental effects of cerebellar tFUS on hippocampal neural dynamics. Through selective blockade of mechanosensitive ion channels with GsMTx4 in either cerebellar cortex or deep cerebellar nuclei (DCN), we established that the cerebello-hippocampal pathway mediated these effects rather than direct acoustic stimulation of the hippocampus. Using extracellular recordings combined with pharmacological interventions, we demonstrated that low-intensity ultrasound applied to the cerebellum reliably modulated hippocampal neuronal activity. Notably, we identified three distinct response patterns (excitatory, inhibitory, and post-inhibitory rebound) and revealed that these patterns were significantly influenced by the pulse repetition frequency (PRF). Our findings showed that higher PRF (10 kHz) preferentially promoted inhibitory responses in hippocampal neurons compared to lower PRF (1 kHz).
Additionally, whole brain cFos expression mapping revealed that cerebellar tFUS activated multiple brain regions beyond the hippocampus, including the hypothalamus, amygdala, and entorhinal cortex. Reduced glutaminase (GLS) and cFos expression in the hippocampal dentate gyrus following cerebellar tFUS, indicating decreased excitatory neurotransmission. By using multi-channel electrocorticography (ECoG) recordings, we showed that cerebellar tFUS at 10 kHz PRF effectively suppressed neural activity across multiple brain regions, with particularly pronounced effects in temporal-hippocampal areas where seizure activity typically originates. Further studies showed that cerebellar tFUS modulates cerebellum-hippocampus dynamics in a PRF-dependent manner, altering local field potential propagation and cross-frequency coupling patterns.
The second part addressed seizure control through cerebellar tFUS intervention. Using a 4-aminopyridine (4-AP) -induced acute seizure model in adult rats, we conducted comprehensive temporal, spectral, and spatial analysis of epileptiform activity. Multi-channel ECoG recordings revealed that administration of 4AP led to elevated spectral power in the alpha (8–13 Hz), beta (13–30 Hz), and gamma (30–80 Hz) bands, while cerebellar tFUS effectively attenuated these increases. Topographical analysis revealed that both seizure hyperexcitability and tFUS suppression were most prominent in temporal-hippocampal regions, establishing spatial specificity. Immunohistochemical analysis showed that glutaminase was significantly increased in the sensorimotor cortex during epilepsy but decreased after cerebellar tFUS. Importantly, we demonstrated superior suppression control efficacy at higher PRF (10 kHz), underscoring the critical importance of stimulation parameter selection for maximizing therapeutic outcomes in this non-invasive neuromodulation approach for epilepsy treatment.
In summary, this thesis investigated cerebellum-targeted tFUS as a promising non-invasive neuromodulation approach, demonstrating its ability to stimulate the cerebellum and thereby modulate downstream neural activity in the hippocampus and broader brain networks, effectively suppressing epileptiform activity. The findings advanced our understanding of cerebello-hippocampus interaction and provided a foundation for developing novel therapeutic interventions for drug-resistant epilepsy that could significantly improve patient outcomes while avoiding the limitations of current treatment modalities.
| Date of Award | 21 Aug 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Chung TIN (Supervisor) |