Multi-modal connectivity of the brain underlying visual hallucinations evoked by high-frequency intracranial stimulations.

BACKGROUND

Visual hallucinations are a common symptom in patients with epilepsy. To the best of our knowledge, there are no studies evidencing the functional and effective networks responsible for different characteristics of these manifestations.

OBJECTIVE/HYPOTHESIS: In this study we aim to perform a multi-modal characterization of the networks underlying visual hallucinations that could be used for clinical purposes.

METHODS

Patients suffering from drug-resistant epilepsy in whom visual hallucinations were elicited by alternating polarity high frequency stimulation (AP-HFS) during stereo-EEG were included. The responses were further classified in 14 clinical categories. We used three methods to characterize functional (FC) and effective connectivity (EC) underlying these clinical responses: non-linear regression analysis using h2 correlation coefficient (FC), magnitude of evoked responses (high-frequency activation - HFA) and phase-locking value (PLV) during stimulation (EC).

RESULTS

We selected 64 consecutive patients in which we applied the AP-HFS and in 22 patients we elicited 130 visual hallucinations. The majority of visual hallucinations were elementary (n = 112), plus (n = 111), static (n = 82), continuous (n = 83) and non-color (n = 74). HFA method shows the highest magnitude of evoked responses in the primary visual cortex and lingual gyrus. PLV analysis reveals a posterior-anterior gradient of connectivity involving both dorsal and ventral stream. The h2 FC highlights the remote prefrontal networks involved in cognitive processing of visual information.

CONCLUSIONS

We evidenced the networks underlying visual hallucinations with different clinical characteristics. These networks are particularly important for planning stereo-EEG explorations in patients with drug-resistant epilepsy and for functional prognosis in posterior acquired lesions and after surgical resections.