Functional MRI and PET

fMRImeasures the brain’s haemodynamic response to neural activity — the BOLD signal. While structural MRI shows what the brain looks like, fMRI shows where it is working under a given task.

Vestibular perception extends beyond the labyrinth and brainstem reflex arcs. The cortical vestibular network spans the temporoparietal junction, posterior insula, superior temporal gyrus, inferior parietal lobule and cerebellar nodulus/uvula — a multisensory hub integrating vestibular, visual and somatosensory input.1

Stimulus paradigms used in fMRI of vestibular processing include caloric irrigation, galvanic vestibular stimulation and optic flow. Resting-state fMRI characterises baseline network connectivity. In PPPD, reduced posterior-insula activity with increased visuo-vestibular connectivity is a recurring finding — a maladaptive shift from vestibular to visual weighting. In vestibular migraine, heightened activation in thalamic and vestibular cortical regions during motion stimuli supports a central sensitisation model.3

The clinical position of fMRI in vertigo is still research-grade. It is not ordered as a diagnostic test for an individual patient. Its value is twofold: it provides the neurobiological substrate that makes “functional” a legitimate clinical category — not a code for “non-organic” — and it generates the evidence that justifies CBT + vestibular rehabilitation + SSRI/SNRI as first- line management for PPPD.

PET visualises metabolic activity using radiotracers, most commonly ¹⁸F-fluorodeoxyglucose (FDG). It is a research tool in chronic vestibular disorders and a clinical tool in selected skull-base and temporal- bone neoplasms.

In MdDS, PET has shown increased glucose metabolism in left entorhinal cortex and amygdala, alongside reduced metabolism in prefrontal and parietal cortices — evidence for maladaptive neuroplasticity in spatial-memory and motion-perception circuits.2In PPPD, FDG-PET work has implicated the parieto-insular vestibular cortex, amygdala and hippocampus, supporting the model of disrupted vestibular– limbic integration.

Outside the functional vestibular disorders, PET-CT is occasionally clinically useful in suspected paragangliomas, skull-base metastases, and rare tumours of the temporal bone — particularly when MRI or CT findings are ambiguous and metabolic information could guide biopsy or surgical planning.

PET is expensive, not widely available, and involves radiation. Reserve it for tertiary research questions, ambiguous skull-base lesions where metabolic information would change management, or — increasingly — for monitoring response to neuromodulatory therapies such as repetitive transcranial magnetic stimulation in refractory chronic vestibular disorders.