Corticobasal Syndrome (CBS) and Progressive Supranuclear Palsy (PSP) are 4R-tauopathies characterized by progressive motor and cognitive decline. These disorders involve widespread disruption of brain networks, particularly those involving the basal ganglia, thalamus, and cortical circuits. This page reviews the network-level dysfunction in these conditions and discusses therapeutic approaches targeting network synchronization, including neuromodulation techniques and pharmacological interventions.
The Default Mode Network (DMN) is a constellation of brain regions active during rest and internally directed cognition. In CBS and PSP, DMN connectivity is markedly disrupted:
The DMN disruption in CBS/PSP differs from Alzheimer's disease patterns, with more prominent involvement of anterior rather than posterior regions[1].
The Salience Network, comprising the anterior cingulate cortex (ACC), anterior insula, and subcortical structures (particularly the striatum and pallidum), is critical for detecting salient stimuli and guiding behavior:
In PSP, salience network disruption correlates with the severity of axial rigidity and postural instability[2].
The Central Executive Network supports working memory, problem-solving, and goal-directed behavior:
Quantitative EEG reveals characteristic abnormalities in 4R-tauopathies:
| Metric | CBS | PSP | Interpretation |
|---|---|---|---|
| Theta power | ↑↑ | ↑ | Cortical dysfunction |
| Alpha power | ↓↓ | ↓ | Attention deficits |
| Beta power | Variable | ↓ | Motor planning impairment |
| Gamma power | ↓ | ↓ | Network integration deficits |
| Coherence | ↓ Frontoparietal | ↓ Interhemispheric | Network disconnection |
Phase locking value (PLV) and phase lag index (PLI) quantify phase synchronization between brain regions:
Magnetoencephalography provides superior spatial resolution for network analysis:
40Hz gamma entrainment is an emerging therapeutic approach that originated from Alzheimer's disease research but has potential applications in 4R-tauopathies:
A landmark study demonstrated that 40Hz gamma entrainment modifies microglial morphology and function:
The microglial effects appear mediated by the TREM2-SYK signaling pathway, which is critical for microglial phagocytosis[4].
While directly studied primarily in AD models, gamma entrainment may benefit CBS/PSP patients through:
rTMS uses magnetic fields to induce electrical currents in cortical regions, modulating network activity:
| Protocol | Target | Frequency | Effects |
|---|---|---|---|
| High-frequency rTMS | M1/DLPFC | 10-20 Hz | Increased cortical excitability |
| Low-frequency rTMS | M1 | 1 Hz | Decreased cortical excitability |
| Theta burst (TBS) | Various | 3 pulses at 5 Hz | Long-term potentiation-like effects |
| iTBS | DLPFC | Intermittent | Cognitive enhancement |
Motor cortex stimulation: Some studies show modest improvement in rigidity and bradykinesia
DLPFC stimulation: May improve executive function and working memory
Parietal stimulation: Experimental approaches for spatial dysfunction
Evidence is limited compared to Parkinson's disease, but rTMS remains a promising therapeutic avenue[5].
rTMS modulates brain networks through:
Both targets modulate basal ganglia-thalamocortical networks but through distinct mechanisms:
Subthalamic Nucleus (STN):
Globus Pallidus interna (GPi):
For CBS/PSP, GPi is generally preferred due to the high cognitive risk in tauopathies[6][7].
DBS normalizes pathological network oscillations:
| Oscillation | Pathological | With DBS |
|---|---|---|
| Beta bands (13-35 Hz) | Elevated | Reduced |
| Theta bands (4-8 Hz) | Variable | Normalized |
| Gamma bands (30-100 Hz) | Reduced | Increased |
| Cross-frequency coupling | Abnormal | Improved |
Emerging approaches use real-time network monitoring:
Excessive glutamate contributes to network hyperexcitability:
GABAergic deficits contribute to network dysfunction:
The goal is to restore glutamate/GABA balance:
The NET is a clinical tool for assessing network function:
| NET Domain | Score Range | Interpretation |
|---|---|---|
| Executive | 0-100 | Higher = better function |
| Memory | 0-100 | Higher = better function |
| Attention | 0-100 | Higher = better function |
| Composite | 0-100 | Overall network health |
| Drug Class | TMS/DBS Interaction | Management |
|---|---|---|
| Anticonvulsants | May reduce rTMS efficacy | Adjust stimulation parameters |
| Benzodiazepines | May enhance sedation | Monitor closely |
| Antidepressants | Generally safe | May need higher rTMS intensity |
| Dopamine agonists | May interact with DBS | Careful parameter tuning |
Combining pharmacological and neuromodulation approaches requires consideration:
| Priority | Intervention | Evidence Level |
|---|---|---|
| 1 | Pharmacological optimization | High |
| 2 | rTMS (targeted) | Moderate |
| 3 | Gamma entrainment | Low |
| 4 | DBS (refractory cases) | Moderate |
Gloor P et al. Default mode network abnormalities in corticobasal syndrome. Neurology. 2020. ↩︎
Daniel SE et al. Salience network disruption in progressive supranuclear palsy. J Neurol Neurosurg Psychiatry. 2019. ↩︎
Torii T et al. EEG biomarkers of network synchronization in atypical parkinsonism. Clin Neurophysiol. 2022. ↩︎
Iaccarino HF et al. Gamma frequency entrainment attenuates amyloid load and modifies microglia. Nature. 2016. ↩︎
Lefaucheur JP et al. Evidence-based guidelines on therapeutic use of transcranial magnetic stimulation. Clin Neurophysiol. 2019. ↩︎
Moriarty H et al. GPi deep brain stimulation for corticobasal syndrome. Mov Disord. 2022. ↩︎
Odekerken VJJ et al. GPi-DBS for progressive supranuclear palsy. Mov Disord. 2023. ↩︎
Chen R et al. Network-targeted stimulation in Parkinson's disease. Brain. 2019. ↩︎
Boasso E et al. Glutamate/GABA balance in tauopathy networks. Neurobiol Dis. 2020. ↩︎