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