Challenges and benefits of multichannel electrophysiology

Advances in techniques for electrophysiological recording as well as in analytical tools are enabling fascinating conceptual and engineering developments in present-day electrophysiological studies of the brain. This workshop will gather together  the scientists contributing to new experimental, theoretical and engineering approaches to this branch of systems neuroscience.

Invited speakers:

• György Buzsáki
• Xiaoqin Wang
• Miguel Nicolelis

György Buzsáki

Rutgers University, USA

Title: Large-scale recording of unit and field activity with silicon probes 

Abstract: How does the brain orchestrate perceptions, thoughts and actions from the electrical and biochemical dynamics of its neurons? Brain organization exhibits distinct patterns at several levels of scale, ranging from the synapses, to local circuits, and to interacting systems. Addressing these challenging issues requires methods with sufficiently high temporal and spatial resolution of neuronal activity in both local and global networks. Although numerous methods, such as macroscopic and microscopic imaging, molecular biological tools and pharmacological manipulations, are available to study brain activity, in the end all these indirect observations should be converted  back into a common currency—the format of neuronal spike trains—to understand the brain’s control of behavior. Specific behaviors emerge from the interaction of neurons and neuronal pools. Studying these processes requires simultaneous monitoring of the activity of large numbers of individual neurons in multiple brain regions. A major goal therefore is to record from statistically representative samples of identified neurons from several local areas while minimally interfering with brain activity.

Micro-machined silicon electrode arrays can record from large numbers of neurons and monitor local neural circuits in behaving animals. Synaptic interactions can be identified, which can serve to segregate excitatory and inhibitory neurons. Current methods allow for recoding neurons as far as 100 µm or more form the soma and thick apical dendrites. In such volume of tissue hundreds or thousands of neurons reside. Isolation and identification of multiple neurons from a single recording site is not possible because all aspects of spikes (duration, amplitude, rise time, decay time) can vary dramatically in different states and behaviors. The use of two or more recording sites allows for the triangulation of distances because the amplitude of the recorded spike is a function of the distance between the neuron and the electrode. Often, this task is accomplished with four or eight closely spaced recording sites. Despite the numerous neuron clustering algorithms developed in various laboratories, in current practice only a small percentage of the available population (typically 5-15 neurons per electrode) can be reliably separated. The remaining neurons are either silent or too small in amplitude, thus preventing reliable separation. Ideally, every part of a probe surface placed in the brain should have monitoring sites. Current industrial technology presently uses almost ten times smaller line features than what is possible at academic institutions. Thus, it is not an unrealistic goal to record from nearly all neurons in a small volume of the brain in behaving animals. Hardware and modeling strategies for increasing neuron yield will be discussed.

Regularly spaced recording sites also allow for the monitoring of extracellular current flow with high spatial resolution and this mesoscopic signal can be used to determine the operation modes of local networks. Recording from representatively large portion of the network also allows for studying behavior-dependent synaptic modification among members of the network.

György Buzsáki - Bio-sketch

Xiaoqin Wang

Johns Hopkins University, USA.

Title: Studying brain functions during natural vocal behaviors using multi-channel wireless recording technology

Abstract: A crucial step in understanding the relationship between the brain and behavior is to study underlying neural mechanisms during natural behaviors. However, many natural behaviors of interest to neurophysiologists are difficult to study under laboratory conditions because such behaviors are often inhibited when an animal is restrained and socially isolated. Even under the best conditions, such behaviors may be sparse enough as to require long-term and simultaneous recording of multiple neurons across several brain areas in order to gather a sufficient amount of data for analysis. One approach to overcome these problems is to combine multi-channel chronic recording techniques with telemetry technology. There are several challenges when taking such an approach to study neural coding mechanisms in mammalian cortex, in particular in animals with three-dimensional movements such as non-human primates. A much desired property of chronic recording techniques is the ability to advance each microelectrode with fine resolutions for isolating individual neurons. A miniaturized broadband telemetry system is necessary to relay multiple channels of behavioral and neural signals with high fidelity and without significantly altering an animal’s behavior. We have developed a unique preparation for chronic multi-electrode recordings from the auditory cortex of free-roaming primates during natural vocal behaviors. I will use our recent studies of neural mechanisms underlying auditory-vocal interactions to highlight the challenges and opportunities in using multi-channel wireless recording technology.

Xiaoqin Wang - Bio-sketch

Miguel Nicolelis

Duke University Medical Center, USA.

Title: Computing with Neural Ensembles

Abstract: In this talk, I will review a series of recent experiments demonstrating the possibility of using real-time computational models to investigate how ensembles of neurons encode motor information. These experiments have revealed that brain-machine interfaces can be used not only to study fundamental aspects of neural ensemble physiology, but they can also serve as an experimental paradigm aimed at testing the design of modern neuroprosthetic devices. I will also describe evidence indicating that continuous operation of a closed-loop brain machine interface, which utilizes a robotic arm as its main actuator, can induce significant changes in the physiological properties of neurons located in multiple motor and sensory cortical areas. This raises the hypothesis of whether the properties of a robot arm, or any other tool, can be assimilated by neuronal representations as if they were simple extensions of the subject's own body.

Miguel Nicolelis - Bio-sketch