Frederick Lenz MD
Professor of Neurosurgery
Professor of Neurosurgery
Figure: Synchrony (Phase Locking Value, PLV) during the pre-stimulus period in beta frequencies (16–24 Hz). A patient with epilepsy had grids implanted over the brain for the investigation of epilepsy. Laser pulses are applied to the hand opposite the grid electrodes. The laser evoked a painful, pin-prick sensation in many but not all trials, although the patient expected that the laser stimulus could be painful or nonpainful. The presence of synchrony (PLV) was analyzed separately for events in which pain was (A) or was not evoked by the laser (B). Statistical significance of synchrony (PLV) between any pair of electrodes was tested by a bootstrap technique, and is indicated a colored line between those electrodes according to the inset. We also calculated the average potential evoked by the laser stimulus (laser evoked potential, LEP, see 1D). The locations of electrodes at which LEP N2 (1D, upgoing) and/or P2 potentials (1D, downgoing) could be recorded in this patient are shown in Figure 1C, relative to intraoperative and MRI anatomy, cortical stimulation results, and phase reversal of the SEP. D, LEPs during pain and non-pain events at the electrode indicated by the arrow in C
The interests of my lab are in the neuronal processes, pathways, and functional connectivity subserving pain, abnormal movements and plasticity. For example, our initial studies of direct recordings from the human CNS demonstrated structures in thalamus and cortex receiving direct input from nociceptors. We then characterized neuronal membrane events processing thermal and pain-related inputs to human thalamic nuclei which project to somatic sensory cortex. These studies suggest that the human thalamus is a processor of sensory input, not merely a relay of such input to cortex. These thalamic studies involve by single unit recordings in patients undergoing surgery for movement disorders. We are now undertaking a number of studies of the impact of lesions on sensory performance. Studies of patients with cortical lesions demonstrate the presence of a hierarchical network of local networks mediating attention to pain. Studies of cortical synchrony characterize functional connectivity within this hierarchical network as a rapidly switching, task specific network sub-serving the attention to painful stimuli. Theses studies involve Local Field Potential recordings directly from the cortex of patients with grids implanted for the treatment of epilepsy. Similar signal analysis techniques are used in studies of movement disorders.