The main purpose of this project is to establish and test a new method that will expand the use of the vitro slice preparations to study spatio-temporal aspects of synaptic integration and the effects of ongoing network activity on neuronal computation. Acute slices are a useful in vitro model for the investigation of nervous system function. However, a significant pitfall is the lack of background neuronal activity. In vivo, neurons maintain a constant level of spontaneous activity which translates into synaptic input for each individual neuron. Synaptic input is known to affect the computational properties of neurons. Currently, in vitro investigation of synaptic integration relies on simulating synaptic activity through current injection at the soma or dendrite. This technique is limited to only one or two injection sites and can not address the still poorly understood dendritic integration of distributed synaptic inputs. In vivo, synaptic inputs constantly arrive at thousands of dendritic sites. In order to investigate synaptic integration at a more realistic level, it is necessary to control large numbers of synaptic inputs in space and time while measuring the response properties of the postsynaptic neuron. Here we propose to develop a new experimental technique, which will allow us to stimulate the dendritic trees of cortical pyramidal cells in vitro with precisely controlled spatio-temporal stimulus patterns. Our specific aims are: Aim 1) Adapt Digital Light Processing (DLP) technology (a matrix of several thousand individually controlled miniature mirrors) to be used as a dynamic photo stimulation (DPS) device. Stimulation occurs through photolytic uncaging of the excitatory neurotransmitter glutamate. UV light for glutamate uncaging will be controlled with DLP, allowing the artifact-free generation of 2-dimensional static or dynamic stimulus patterns. Aim 2) Use dynamic photo stimulation (DPS) to test the influence of synchronous "background" input on gain in neocortical neurons. We will use DPS to generate precisely defined spatio-temporal input patterns on the dendritic tree of cortical pyramidal cells while measuring neuronal responses. Acute slices are the method of choice for many studies related to human health, such as pharmacological studies of drug abuse or the evaluation of memory enhancing drugs. The improvements brought about by our new method will significantly expand the range of questions that can be addressed in acute slice preparations. The use of living slices of brain tissue to study the nervous system is the method of choice for many studies related to human health, such as pharmacological studies of drug abuse or the evaluation of memory enhancing drugs. The improvements brought about by the new method we propose to develop here will significantly expand the range of questions that can be addressed in living brain slice preparations. [unreadable] [unreadable] [unreadable]