EEG-ECeG coherence mapping of human cerebro-cerebellar projections

Abstract

The cerebellar and cerebral cortices are powerfully connected via reciprocal, crossed projections which mediate their coordination in motor, cognitive and affective processes. In the present paper we demonstrate non-invasive imaging of crossed cerebro-cerebellar connectivity by means of wavelet coherence. In a sample of six healthy adult subjects, we recorded EEG and the electro-cerebellogram (ECeG) with a 10% cerebellar extension montage during voluntary left and right index finger and foot movements. EMG was also recorded from finger extensors and flexors and from the tibialis anterior and soleus muscles and was used to generate triggers for movement related averaging (-2000 to + 2000 ms). Wavelet power and EEG-ECeG coherence were computed over the 4 s epoch for each electrode and for statistical analysis both cerebral and cerebellar grids centred around Cz and SIz. Movement related changes were observed in both cerebral and cerebellar power, most significantly in the high delta band (1.5 to 3 Hz). Significant movement related change in d-band EEG-ECeG coherence was also observed and to a lesser extent a-decoherence. Of particular note, when lateralised seeds were selected (C1 vs C2 and PO11 vs PO12) the low-frequency (d, q, a, b) coherence was distributed contralaterally for both cerebral and cerebellar seeds, likely reflecting the underlying crossed cerebro-cerebellar projections. However, the two projections differed in their spatial distribution whereby the cerebellar (PO11/PO12) seeded coherence was concentrated towards the cerebral midline while the cerebral (C1/C2) seeded coherence was distributed away from the cerebellar midline. The cerebral (C1/C2) seeded coherence also extended anteriorly to temporal leads suggestive of temporal lobe involvement. Evidence was also apparent of a distinct high-frequency (VHF/UHF) crossed projection which differed again in its spatial distribution. These findings further support the value of recording cerebellar ECeG and demonstrate its potential to contribute to the understanding of cerebro-cerebellar function and dysfunction.