Z. Nadasdy, D. A. Wagenaar, and S. M. Potter: Attractor dynamics of superbursts in living neural networks. SFN 2003, New Orleans, LA,
2003.
ABSTRACT
Attractor dynamics of superbursts in living neural networks
Z. Nadasdy; D.A.Wagenaar; S.M.Potter
Many brain processes, from odor recognition to motion sequence generation, can be described in terms of dynamic attractors. Here we explore the emergence of attractor dynamics in the spiking activity of neuronal cultures growing on multi-electrode arrays (MEAs). We recorded spiking activity through 58 surface electrodes, continuously for 24h periods. Using superparamagnetic clustering (SPC), we were able to isolate in excess of 200 units per culture. The most prominent feature of the spontaneous firing behavior of these cultures is population bursting. In contrast with earlier reports, we find that many cultures generate ""superbursts"" during development with a complex internal dynamics. While cultures displaying simple population bursts exhibit varying spatio-temporal patterns, superbursts have much more stereotyped dynamics for a given culture: - The order in which different cells are engaged in bursts is highly conserved from burst to burst, and is independent of the firing rate of individual cells. - Principal component analysis (PCA) reveals that consecutive bursts trace similar orbits through activity space. - Burst composition is more conserved across successive superbursts than within a superburst, indicating a superburst level coordination of spike dynamics. These results demonstrate that even in dissociated culture, cortical neurons can form networks that exhibit rich dynamics with recurring structure at timescales far beyond those of individual action potentials. Since networks with attractor dynamics express learning capability, we plan to utilize this feature to control robots ('animats', or 'hybrots'). Feedback stimulation derived from the environment of the robot will modify the attractor landscape enabling the culture to learn new behavior.
D. A. Wagenaar, and S. M. Potter: Parameters for voltage- and current-controlled stimulation of cortical cultures through multi-electrode arrays. SFN 2003, New Orleans, LA, 2003.
ABSTRACT
Parameters for voltage- and current-controlled stimulation of cortical
cultures through multi-electrode arrays
D. A. Wagenaar; S. M. Potter
We electrically stimulate cultures of dissociated neurons from rat cortex growing on MEAs, with two goals: 1. We study the influence of patterned stimulation on the development of functional connectivity in living neural networks. 2. We use electrical stimuli to convey an animat's or hybrot's sensory input to the culture which is its brain. For both, detailed knowledge of the impact of different stimulation parameters is indispensible. We find that cathodic current pulses are effective stimuli. Both very short but strong (50 uA x 20 us), and very weak but prolonged (5 uA x 1 ms) stimuli elicited network response. No responses to any anodic pulses were observed. While current-controlled pulses are attractive, the required hardware is difficult to implement for many electrodes. Therefore, we also studied voltage-controlled pulses. Biphasic, anodic-first, square waveforms were most effective, due to the cathodic current spike accompanying the voltage transient between the two phases. The response patterns to these stimuli remain stable for several days in mature cultures. On the other hand, by sending in trains of stimuli at frequencies between 0.1 Hz and 100 Hz, we determined that responses are relatively suppressed at rates above 1 Hz. During continued high-frequency stimulation on one electrode, responses to stimulation on another electrode are not reduced, so we think this suppression is due to ionic or vesicle depletion in directly stimulated cells. These findings drive the design of our next generation of stimulators. Moreover, the parameter space of stimuli that retain their efficacy upon repeated presentation is an essential resource for studying the influence of continuous stimulation on development. It could also benefit animal studies involving extracellular stimulation, and have clinical implications for deep brain stimulation and control
of epilepsy.
PANEL
R. Madhavan, D. A. Wagenaar, and S. M. Potter: Multi-site stimulation quiets bursts and enhances plasticity in cultured networks. SFN 2003, New Orleans, LA, 2003.
ABSTRACT
Multi-site stimulation quiets bursts and enhances plasticity in cultured networks
R. Madhavan; D. A. Wagenaar; S. M. Potter
We study stimulus-induced plasticity and information processing in dense dissociated monolayer cultures of E-18 rodent cortical neurons grown on Multi-electrode arrays (MEAs). Dishwide spontaneous bursts, or ""barrages"" dominate the activity of such networks. We hypothesize that these spontaneous barrages are due to lack of natural input and are wiping out the effects of potential plasticity-inducing stimuli. We compensate for the absence of natural input by applying a continuous stream of weak electrical stimuli at multiple electrodes. With such distributed sequential stimulation, we have successfully reduced the contribution of spontaneous barrages to the total firing rate of the network. The goal of this work is to investigate whether such controlled cultures are more conducive for the induction of plasticity at the network level. A 10Hz sequence of stimuli applied at 10 electrodes reduced the duration and rate of occurrence of barrages. With this 'quieted' level of activity as baseline, a tetanic pulse train is applied to two other electrodes, which induces a spatially distributed pattern of LTP and LTD. We study the temporal structure of spike trains and the activity-dependent changes in the reliability and reproducibility of spike patterns evoked by a probe stimulus. We use these patterns in the control of animats or hybrots (hybrid neural-robotic creatures). We find that in cultures controlled by continuous background stimulation throughout the experiment, tetanic stimulation induces a stronger and more sustained change in probed response. Changes in neural plasticity can be mapped to changes in the animat's behavior, enabling us to study
how information is encoded within an embodied living neural network.
D. A. Wagenaar, R. Madhavan, and S. M. Potter: Stimulating news for MEA enthusiasts. SIMEA 2003, Denton, TX, 2003.
ABSTRACT
R. Madhavan, D. A. Wagenaar, C.-H. Chow, and S. M. Potter: Control of bursting in dissociated cortical cultures on multi-electrode arrays. SIMEA 2003, Denton, TX, 2003. .
ABSTRACT
T. B. DeMarse, D. A. Wagenaar, S. M. Potter: The neurally-controlled artificial animal: a neural-computer interface between cultured neural networks and a robotic body. SFN 2002, Orlando, FL.
ABSTRACT
THE NEURALLY-CONTROLLED ARTIFICIAL ANIMAL: A NEURAL-COMPUTER INTERFACE BETWEEN CULTURED NEURAL NETWORKS AND A ROBOTIC BODY
T.B. DeMarse*; D.A. Wagenaar; S.M. Potter 1. Biomedical Engineering, Georgia Tech, Atlanta, GA, USA 2. Physics, California Institute of Technology, Pasadena, CA, USA 3. Biomedical Engineering, Georgia Tech, Atlanta, GA, USA
Living neural networks of dissociated rat cortical cells were cultured on a 60 channel multi-electrode array from MultiChannel Systems and interfaced to a robotic body (a Khepera II by K-Team). The spatio-temporal pattern of neural activity was measured in real-time to produce movements of the mobile robot via a custom computer interface. The Khepera's onboard IR sensors acted as the sensory system, measuring distance from eight IR emitters positioned around a circular pen. This sensory information was then fed back into the neural culture by varying the temporal structure of neural stimulation as a function of distance to each sensor. Because these multi-electrode arrays allow simultaneous electrical, chemical, and optical access to a population of neurons, we can conduct detailed investigations into the mechanisms that produce changes in neural activity as a result of feedback at the microscopic and macroscopic levels. Because we can culture primary cortical neurons for many months, we can examine plasticity in vitro over much longer periods than previously possible. With this simple system we hope one day to develop more advanced computational algorithms in living neural networks, leading to a greater understanding of how these networks can process and encode information, and control behavior. Supported by: National Institute of Neurological Disorders and Stroke, R01 NS38628
Citation: T.B. DeMarse, D.A. Wagenaar, S.M. Potter. THE NEURALLY-CONTROLLED ARTIFICIAL ANIMAL: A NEURAL-COMPUTER INTERFACE BETWEEN CULTURED NEURAL NETWORKS AND A ROBOTIC BODY Program No. 347.1.
D. A. Wagenaar, T. B. DeMarse, and S. M. Potter: Response properties of cultured cortical networks as a substrate for the study of learning in vitro. Int. Conf. Cognitive and Neural Systems, Boston University, Boston, 2002. ABSTRACT Response properties of cultured cortical networks as a substrate for the study of learning in vitro D. A. Wagenaar*×, T. B. DeMarse+, S. M. Potter+ *Dept. of Physics, + Div. of Biology; California Institute of Technology.
× Caltech 103-33, Pasadena, CA 91125; wagenaar@caltech.edu
Our lab pursues the study of learning in vitro by connecting neuronal cultures with simulated bodies in computer generated environments. We connect the output of a set of 60 electrodes embedded in a culture dish on which we grow dense networks of embryonic (E18) rat cortical neurons to the motor control of such artificial animals (or animats). Information from their sensory organs is sent back to the dish in a closed feedback loop by electrically stimulating through the same substrate electrodes. Our recording, processing and stimulation system can provide feedback with a delay of less than 100~ms.
As an essential step towards this goal, we have been studying the response properties of these living neuronal networks to simple electrical stimuli. In absense of stimulation, the cultures' major mode of activity is global bursts, which show interesting dynamics at the timescale of minutes and large variability at the timescale of days to months. Responses to electrical stimuli consist of spikes in the first 20 ms post-stimulus timed with deep sub-millisecond precision, followed by less precisely timed spikes and occasional induced global bursts. These responses are typically stable over many days of continuous probing.
The study of short-latency responses became possible thanks to an algorithm we recently developed to suppress the very large artifacts that plague recordings shortly after stimulation. The algorithm locally fits polynomials to the shape of the artifact and can remove artifacts ten times the size of action potentials from the recorded trace in real-time on standard PC equipment.
We found that precisely timed responses, unlike other evoked activity, persist in the presence of NMDA and AMPA synapse channel blockers, indicating that they originate directly from the stimulated neuron. However, their reliability and latency do change as a result of blocking synapses, showing that synaptic influences are important. Non-monotonicities in response reliability vs stimulation voltage are further evidence for network influences.
These results will serve to help us to intelligently design sensory-motor mappings for our neurally controlled animats.
Work is currently underway to characterize the response to pairs of stimuli and the associated inter-pulse-interval dependence, which several groups have found to be of major significance in inducing synaptic plasticity.
PANEL
D. A. Wagenaar, T. B. DeMarse, J. Pine, and S. M. Potter: Precise timing in early response to electric stimulation in dense cultures of cortical neurons . Proc. Mathematics in Molecular Biology, Santa Fe, 2002. Precise timing in early response to electric stimulation in dense cultures of cortical neurons D. A. Wagenaar*×, T. B. DeMarse+ , J. Pine *, S. M. Potter+ *Dept. of Physics, + Div. of Biology; California Institute of Technology.
× Caltech 103-33, Pasadena, CA 91125; wagenaar@caltech.edu
Using a novel algorithm for stimulation artifact suppression in micro-electrode array (MEA) recordings based on local regression to artifact shape [1], we are studying short latency responses to electrical stimulation in dense cultures of rat cortical neurons.
In the time window that was previously inaccessible due to artifacts, 1.5-20 ms post-stimulus, we observe spikes (extracellular action potentials) with timing precisions of 0.05-0.15 ms. These spikes are not abolished by blocking glutamatergic synapses, suggesting that they are the result of direct axonal propagation. Such directly evoked responses are observed on electrodes all the way across the array from the stimulation site (1.5 mm distant), and at latencies up to 15 ms. None of these response components are 100% reliable, but many occur in 50-75% of stimulation trials. Evoked responses on different electrode channels are mostly independent, and require different minimum stimulus voltages, indicating that several axons or somata are stimulated by the (single) stimulation electrode.
From 5 ms post-stimulus, spikes are also observed with timing precisions of 1-5 ms. Blocking glutamatergic synaptic transmission confirms that these are mostly postsynaptic from the stimulated neuron(s).
Blocking glutaminergic synapses does modify many of the precisely timed response components, even the very early ones, by sharpening up the timing, shifting the latency or changing the reliability. This indicates that ongoing synaptic activity plays an important modulatory role in the generation of directly evoked firing. We are currently investigating how patterned stimulation may be used to shape ongoing activity and thus to gain control over the modulation, which will be an important step towards realizing the computational capabilities of living neuronal networks [2].
This work was supported by grant RO1-NS38628 from the NINDS, and by the Burroughs-Wellcome Fund/Caltech Computational Molecular Biology program.
References
[1] D. A. Wagenaar and S. M. Potter, Stimulus artifact suppression by local polynomial approximation, submitted. [2] T. B. DeMarse, D. A. Wagenaar, A. W. Blau and S. M. Potter, The neurally controlled animat: biological brains acting with simulated bodies, Autonomous Robots 11 (2001), 305-310. D. A. Wagenaar, T. B. DeMarse, J. Pine, S. M. Potter: Development of complex activity patterns in cortical networks cultured on multi-electrode arrays. Soc. for Neuroscience 31st annual meeting, San
Diego, 2001.
ABSTRACT
Development of complex activity patterns in cortical networks cultured on multi-electrode arrays
Daniel A. Wagenaar, Thomas B. DeMarse, Jerome Pine*, Steve M. Potter
We are looking for regularities in the firing patterns of cultured cortical networks, which we plan to use to control the behavior of a simulated animal (the Neurally Controlled Animat; Potter et al., SFN2000 abstract 467.20). To this end, neurons and glia from E18 rat cortex were dissociated and densely plated on planar MEAs (multi-electrode arrays) with 60 electrodes. We made daily recordings from each dish for 30 consecutive days starting one day after plating. Recurring dynamic patterns were observed on many timescales, from less than 100 ms through minutes.
Single-cell action potentials were observed from the second day in vitro. Dish-wide bursts occurred from the fifth day, earlier than previously reported. As the cultures matured, bursts became increasingly frequent, and isolated spikes, while increasing in absolute numbers, became an ever smaller part of the dishes' activity. The dishes produced global bursts between one and 30 times per minute. Often, periodicity was maintained with few interruptions for several minutes.
Most global bursts were found to be immediately preceded (within 50 ms) by elevated activty of neurons near only one or a few electrodes. These initiator sets changed as the cultures developed. Recordings that showed the highest global burst frequencies, often exhibited switching between very low (3/min) and very high (upto 60/min) burst frequencies, in cycles of up to 3 minutes.
These observations will provide the basis for a study of the effects of chronic (continuous) electrical stimulation on cortical networks developing in vitro.
This work is supported by grant #R01NS38628 from NIH/NINDS, and by the
Burroughs-Wellcome/Caltech CMB fund.
PANELS
D. A. Wagenaar, T. B. DeMarse, and S. M. Potter: A toolset for realtime analysis of network dynamics in dense cultures of cortical neurons . 7th JSNC, University of California at San Diego, La Jolla, 2001. PANEL