GABAergic cortical network physiology in frontotemporal lobar degeneration

Area of Science:

• Neuroscience
• Neurodegenerative Diseases
• Computational Psychiatry

Background:

• Frontotemporal lobar degeneration (FTLD) encompasses heterogeneous clinical syndromes like behavioral variant FTD (bvFTD) and progressive supranuclear palsy.
• Shared behavioral, cognitive, and physiological features across FTD subtypes may stem from common deficits in major neurotransmitters, notably γ-aminobutyric acid (GABA).
• Understanding these neurotransmitter deficits is crucial for developing targeted therapies.

Purpose of the Study:

• To quantify GABAergic impairment in patients with FTD and progressive supranuclear palsy.
• To investigate the restoration of GABAergic function using dynamic causal modeling (DCM) following treatment with a GABA reuptake inhibitor.
• To establish a link between neurophysiological deficits, GABA levels, and clinical manifestations in FTD.

Main Methods:

• A double-blind, placebo-controlled crossover pharmaco-magnetoencephalography (MEG) study involving 17 bvFTD patients, 15 progressive supranuclear palsy patients, and 20 healthy controls.
• Participants underwent MEG with an auditory oddball paradigm on placebo and with tiagabine (a GABA reuptake inhibitor).
• Biophysical modeling (DCM) was used to analyze neuronal network function, complemented by structural MRI, neuropsychological assessments, and ultrahigh-field MR spectroscopy for GABA concentration measurement.

Main Results:

• GABA concentration was reduced in patients with FTD compared to controls.
• DCM identified deficits in frontotemporal processing, with top-down connectivity correlating with cognitive and behavioral changes.
• Tiagabine administration modulated local circuits, with effects dependent on baseline GABA levels, demonstrating GABA's role in neural function and treatment response.

Conclusions:

• Dynamic causal modeling can elucidate neurobiological mechanisms in human neurodegenerative diseases like FTD.
• GABAergic deficits contribute to the pathophysiology of FTD, and targeting these deficits shows potential for therapeutic intervention.
• This approach can inform personalized drug selection and patient stratification for clinical trials in FTD.