Motor functions and connectivity of the superior colliculus.

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In our preceding studies we demonstrated the existence of reach-related signals in the intermediate and deep layers of the human superior colliculus (SC), in a transition region to the mesencephalic reticular formation (MRF). Because of this localisation we introduced the label "SC-MRF region". Using fMRI we also demonstrated a lateralisation of reach-related signals depending on the active arm and distinguished reach-related signals unequivocally from visual stimulation of the SC. In the last two years, unspecific movements of the arms, hands, and fingers up to full reaching movements have been elicited by pharmacological and electrical stimulations of this region in non-human primates in two studies. Addressing the neural substrates of cervical dystonia, another study in monkeys demonstrated the attentuation of a torticollis that was induced by inhibition of the substantia nigra through a pharmacological treatment of the deep SC. Transferring this observation to the functional context of our studies let us assume that the functions and connectivity of the SC could have a clinical relevance for the occurrence of focal dystonias and other movement disorders of the upper limb. However, essential characteristics of the human SC-MRF region are currently unknown. Previous studies of this region in monkeys and humans focused on visually guided reaching. Therefore, it is unclear whether the SC-MRF also contributes to the processing of other movement types, e.g. somatosensory guided movements or coordinated finger movements without transport movements of the arm. Furthermore, the functional and anatomical connections of the human SC-MRF are completely unknown and even in monkeys its connectivity is mostly unknown. The first main goal of our project is a specification of those motor functions that are associated with activity of the SC-MRF region. Our second main goal is an exhaustive description of this region's anatomical and functional connectivity within the human motor networks, ranging from cortical motor areas to the cervical spine.