Electrophysiologists studying the brain must often choose whether to observe the forest or the trees: electroencephalogram (EEG) and local field potentials (LFP) measure macroscopic oscillations in large populations of neurons, while single unit recordings measure microscopic potentials generated by single cells. We propose to examine the relationship between these two in motor cortex, where high frequency (10- 45Hz) oscillations are commonly observed. These oscillations are clearly modulated by behavior, but some authors have argued that they are a symptom of cortical inactivation in the absence of movement, while others have suggested they serve a role in sensorimotor integration across distributed regions of cortex. It is well known that oscillations affect the timing of action potentials generated by many motor cortical cells, but the significance of this effect - which occurs at the intersection of two levels of analysis - is not well understood. We propose to examine the behavioral relevance of these oscillations and the effect of oscillatory structure on the information encoded and communicated in neuronal spikes. We will record single units and LFPs from motor and pre-motor cortex using high-density, 100-electrode arrays implanted in primary motor, ventral pre-motor, and dorsal pre-motor cortex in behaving monkeys. These monkeys have been trained to perform simple reaching tasks that involve repeated movements to visually-instructed targets. In an initial set of experiments, we will attempt to dissociate the oscillatory activity associated with selecting and planning a movement with the activity associated with maintaining a stationary posture. In a second set of experiments, we will examine the impact of LFP power and phase on the kinematic information encoded in neural spiking. In a third set of experiments, we will examine the effect of oscillatory structure on functional connectivity using both statistical methods and more directly by assessing the propagation of electrical stimulation applied at different phases of the ongoing global oscillation. Public Statement: Global oscillations are a hallmark of brain activity in both sickness and in health;they have been related to higher order functions such as attention, sensation, and memory, and they play an important role in pathologies such as Parkinson's disease and epilepsy. Despite being a ubiquitous feature of brain activity, it is not clear what effect, if any, oscillations have on neural information processing. We will record brain activity in behaving monkeys using high-density multi-electrode arrays, and use this data to assess the effects of oscillations on the neural circuitry involved in generating motor behavior.
| Reimer, Jacob; Hatsopoulos, Nicholas G (2010) Periodicity and evoked responses in motor cortex. J Neurosci 30:11506-15 |
