Stimulation of Forel's field during stereotaxic operations in the human brain

Evolution of Neuromodulation

“…However, there was concern that lesions in the subthalamic nucleus might produce the complication of hemiballism, so it was never a popular target. In 1964, another subthalamic area, Forel's fi eld (campus Forelli) was reported to produce results as good as pallidotomy, a procedure that Spiegel et al [16] termed campotomy, which they felt was superior to pallidotomy with less risk. In a direct comparison study in 1969, campotomy was found to be better than thalamotomy [64] .…”

“…Stereotactic surgery was used very early for epilepsy, and a change in EEG or electrocorticogram was seen during stimulation of subcortical structures, such as thalamus [15] or globus pallidus. Prior to making lesions in Forel's fi eld, stimulation was used to identify when the electrode progressed to the oculomotor fi bers just deep to the caudal extent of Forel's fi eld, so the lesion could be made just above the site where stimulation provoked eye movements [16] .…”

History Repeats Itself

“…This was particularly useful when the target lay in the brainstem where eloquent tracts lie close together, and was, for instance, part of the procedure of localizing the electrode in campotomy reported in 1964 [58]. Stimulation just below the target in the prerubral field most often caused extraocular movement of just the ipsilateral eye, presumably because of stimulation of the emerging splayed out oculomotor fibers, which demonstrated the most inferior location of the lesion.…”

Stereotactic Surgery –T he Past and the Future

“…There were still those, however, who questioned where the ideal target lay [39]. For instance, Spiegel and Wycis moved their target to Forel's field, again to target the pallidofugal fibers after they had emerged [40,41].…”