Journal id: CSMR_A_294481
Corresponding author: JOSHUA C. BRUMBERG
Title: Barrels by the sea: Barrels XX meeting report
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Somatosensory and Motor Research, Vol. ??, No. ?, Month?? 2008, 1–4
Barrels by the sea: Barrels XX meeting report
Department of Psychology, Queens College, CUNY, New York, USA
(Received 22 22 22; revised 22 22 22; accepted 22 22 22)
The 20th annual Barrels meeting brought together researchers who utilize behavioral, physiological, anatomical, and
molecular techniques to understand the structure and function of the barrel system. Barrels XX featured talks on the role
inhibition has in shaping cortical responses within the barrel system, the molecular cues that influence the development of
the whisker-to-barrel system, and the synaptic plasticity that can shape responses within the system. The meeting highlighted
why the whisker-to-barrel system is an ideal model to investigate the development of cortical circuitry and how its
functioning can influence behavioral responses.
Keywords: Barrel, whisker, vibrissa, cortical circuits
On the first two days of November 2007, the 20th
annual Barrels meeting was convened by the sea in
the Sherwood Auditorium of the Museum of
Contemporary Art San Diego, La Jolla campus.
Barrels XX like all previous meetings brought
together researchers who utilize the whisker-to-
barrel system as a model to understand neural
development, plasticity, physiology, and anatomy.
The first session on the role of cortical inhibitory
circuits was moderated by Randy Bruno (Columbia
University) who defined some of the important issues
surrounding how inhibitory circuits are defined
anatomically/physiologically and how they are
engaged by sensory stimulation. Dr Bruno high-
lighted the differences in action potential waveforms
between excitatory and one class of inhibitory
neurons within the barrel and how these cell types
have different response properties. For example, the
inhibitory fast spiking units having poorer angular
tuning and more multi-whisker receptive fields which
are correlated with differences in the number and
locations of the thalamic inputs on to these pheno-
types. Diego Contreras (University of
Pennsylvania) highlighted several different roles that
inhibition has in the barrel circuit. He emphasized
the role inhibition has in determining over what time
period a neuron integrates afferent information,
demonstrating that neurons within thalamic recipient
zones such as the barrel have much shorter windows
then neurons residing in the supragranular layers.
Interestingly, intracellular recording studies in vivo
revealed that increasing the velocity of whisker
deflection increases the magnitude of the evoked
excitatory postsynaptic potentials (EPSPs) and inhi-
bitory postsynaptic potentials (IPSPs), but does not
affect the timecourse of the EPSP/IPSP sequence. In
other words, there is no change in the window of
opportunity during which EPSPs can exert their
influence before they are damped down by disynaptic
inhibition after 5–7 ms. Dr Contreras studies argued
that whisker-evoked IPSPs have little to do with the
finding that when recording from the columnar
whisker, prior deflection of an adjacent whisker
decreases the columnar whisker response. Next,
Edward Callaway (Salk Institute for Biological
Sciences) emphasized that there are many different
types of inhibitory interneurons each with their own
characteristic synaptic inputs and axonal targets.
Using laser uncaging of glutamate, Dr Callaway
demonstrated that interneurons found within a
specific cortical lamina received inputs from some,
but not all the other cortical laminae and their axons
Correspondence: J. C. Brumberg, Department of Psychology, Queens College, CUNY, 65–30 Kissena Boulevard, Flushing, NY 11367, USA. Tel: þ1 718 997
3541. Fax: þ1 718 997 3257. E-mail:
ISSN 0899–0220 print/ISSN 1369–1651 online ß 2008 Taylor & Francis
DOI: 10.1080/08990220801943159
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might only target specific laminae/sub-laminae.
For example, using transgenic mice expressing
GFP (green fluorescent protein) specifically in
interneuron subtypes, it was revealed that
Martinotti cells and bipolar cells receive the majority
of their excitatory inputs from layers 2/3. His results
argued for a dramatic amount of specificity of the
connections made onto and originating from cortical
interneurons. Finally, Anna Devor (University
of California San Diego) focused on the mechanisms
driving the hemodynamic response in the barrel
following whisker deflections. Using physiological
and hemodynamic measures, Dr Devor demon-
strated that the greatest change in arteriole diameters
was centered on the area of greatest cortical
activation. In contrast, the surrounding blood vessels
constricted. Surprisingly, the hemodynamic response
was uncorrelated with simultaneously recorded local
field potentials. Imaging techniques indicated that
there was a large response observed contralateral
to the whisker deflection followed by responses seen
in the ipsilateral cortex delayed by approximately
20 ms which was characterized by a constriction
of the blood vessels. She concluded that the
hemodynamic response was due to the release of
vasoactive peptides by interneurons not due
a metabolic demand or increases in multi-unit
activity/local field potentials. The morning’s session
emphasized the diverse roles inhibition has in
shaping the responses of neurons and the associated
blood flow to the barrel.
After a brief break there followed a series of short
platform talks moderated by Martin Deschenes
(Laval University). Kentaroh Takagaki (Leibniz
Institut fu
r Neurobiologie) demonstrated using
voltage-sensitive dyes that neuronal activity is
highly correlated with recorded EEG and that the
overall activity of the neurons imaged does not
encode for the direction a whisker is deflected.
Whisker stimulation evokes waves of activity that
appear to encode the presence but not any char-
acteristic of the stimulus. Illan Lampl (Weizmann
Institute of Science) focused on how adaptation to
whisker stimulation influences the balance of excita-
tory vs inhibitory inputs onto neurons. Using in vivo
whole cell recording techniques from layer 2/3 and
4 neurons, it was observed that the incoming PSPs
became slower and broader due to greater adaptation
of disynaptic IPSPs. Specifically, excitatory inputs
were found to initially decrease in magnitude faster
but reached a steady state whereas inhibitory inputs
adapt throughout the stimulus train. Interestingly,
adaptation was found to be greater in layer 2/3
compared to layer 4 neurons. John Curtis
(University of California San Diego) looked at how
whisker kinematics and stimulus contact are reflected
in the spike trains of neurons in rat barrel cortex.
Using rats trained to whisk and make contact with
a stimulus as well as those trained to whisk in air,
most neurons responded to stimulus contact, but a
significant population (20%) only responded when
the contact occurred at a specific phase of the
whisking cycle. This signal may allow the animals
to estimate the location of an object in space.
A shunting inhibition model with three compartment
cells (dendrites, soma, spike generator) was capable
of fitting experimental data.
The afternoon session initiated with a series
of short talks moderated by Mitra Hartmann
(Northwestern University). Cornelius Schwarz
(University of Tubingen) argued that there
were two perceptual channels encoding whisker
movement: one that is conveyed by slowly adapting
receptors and is activated by high amplitude low
velocity sweeps and the other is selectively activated
by low amplitude high velocity impacts and
is conveyed via rapidly adapting receptors. Ideal
observer analysis revealed that a single spike is capable
of reliably encoding the presence of a stimulus but
three spikes are required to match psychometric data.
Vivek Khatri (Hunter College) demonstrated that
a subpopulation of trigeminal ganglion neurons
encode whisker kinematics in head-fixed rats trained
to whisk in air. Christian de Kock (Erasmus
University Medical Center) using juxtacellular
recording/labeling techniques in head-fixed rats
whisking in air showed that the firing rates of cortical
neurons varied as a function of the lamina that the
soma was situated. Layer IV neurons showed no
correlation with whisking, layer V thick tufted
neurons decreased their firing in response to whisk-
ing, and layer V thin tufted neurons increased their
firing rates with whisking. Most of the responsive
neurons fired preferentially during the protraction
phase of the whisking cycle. Ehud Ahissar
(Weizmann Institute of Science) focused on the
issue of object encoding in space. He posited that
radial coding (distance from the head) was based on
a firing rate code since firing rate decreased as a
whisker encounters an object close to the base to its
tip. Where an object was in the horizontal place was
based on a time code. Finally, vertical coordinates
are encoded by a spatial code (which whiskers
contacted the object, e.g., A row vs E row).
Tony Prescott (University of Sheffield) using
high-speed videography demonstrated that whisking
changes when a rat contacts an object with its
whiskers, resulting in decreases in whisk amplitude,
decreases in the spread of the whiskers, and increases
in the time that it takes to reach maximum
protraction. The net result of these adaptations is
to maximize sampling of the contacted object.
Hajnalka Bokor (Institute of Experimental
Medicine, Hungary) demonstrated that the local
2 R. L. Ramos & J. C. Brumberg
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field potential in the barrel cortex was more
correlated with the activity in the posterior medial
nucleus (POm) of the thalamus compared to the
ventral posterior nucleus (VPm). Silencing the cortex
via initiation of spreading depression resulted in no
activity in POm, but VPm was unaffected.
Thursday late afternoon saw the first Barrel data
blitz where researchers were given exactly 3 min to
present their latest results. This was followed by
a poster session and dinner at the La Jolla Women’s
Club across the street from the Museum.
Friday morning started with a session on the
molecular development of the barrel system led and
moderated by Jochen Staiger (Albert-Ludwigs
Universita¨t). Dr Staiger provided an overview of
the basic processes underlying neural development
including: neural induction, polarity/segmentation,
migration, determination/differentiation, axon gui-
dance, target selection, synapse formation, and
finally refinement of synaptic connections.
Yashushi Nakagawa (University of Minnesota)
focused on the cues leading to the development of
specific thalamic nuclei. Thalamic sensory nuclei are
generated in the rostral thalamus and the gene
Olig3 marks the entire thalamic progenitor zone.
In contrast, Mash1 and NKX2.2 demark the rostral
zone. The genesis of specific thalamic nuclei and the
migration of cells from the progenitor zone to their
final resting place is influenced by gradients of Dbx1
(caudal 4 rostral) and Olig2 (rostral 4 caudal).
Ed Lein (Allen Institute for Brain Science) provided
a detailed description about how the Allen Institute
for Brain Science went about the task of screening
the mouse brain for all its known gene products as
well as preliminary data from a project to do the same
for the human brain. The data contained within the
generated database is being used to determine the
regional expression of specific genes to determine
if specific cortical areas, for example, primary
somatosensory cortex (S1), have distinct gene
profiles. Approximately 3000 genes show heteroge-
neous expression in S1 when compared to other
cortical areas. Among this list, neurons in layer V and
VIb have the most specific/restricted gene profiles.
Approximately, 155 genes found in this list delineate
interneurons. Peter Kind (University of Edinburgh)
focused on the role that phopholipaseC-Beta1
) has on the development of the barrel
cortex. The gene is present early in development,
but not during later stages and its targeted deletion
results in the absence of the barrel pattern
using cell makers, despite normal segregation
of thalamocortical afferents. Dr Kind went on to
demonstrate that many of the key steps of
barrel formation (pathfinding by thalamocortical
afferents, dendritic orientation, and synapse forma-
tion) are all dependent upon glutamate receptors.
Gord Fishell (New York University), using genetic
and physiologic techniques, was able to elegantly
show that different phenotypes of GABAergic inter-
neurons develop in distinct proliferative regions of
the embryonic forebrain. For example, double
bouquet and neurogliaform cells which both dis-
charge regular spikes derive from the caudal gang-
lionic eminence whereas those with the fast spiking
phenotype (basket, Martinotti, and chandelier cells)
originate from the medial ganglionic eminence.
The Friday morning session was concluded with a
series of short talks moderated by Mary Ann Wilson
(Johns Hopkins University). Amy Nakashima
(University of Calgary) showed that Zn
within the barrel cortex was influenced by the
sensory environment. Rats in deprived (C-row
trimmed) conditions showed elevated Zn
in the deprived barrels. Interestingly, animals reared
in an enriched environment for at least 1 week also
showed an increase in Zn
staining. Malgorzata
Kossut (Nencki Institute for Experimental Biology),
using a conditioning paradigm where whisker stimu-
lation was associated with a tail shock, demonstrated
that the 2-deoxyglucose representation in layer IV for
the associated barrel expanded. Following the train-
ing there was an increase in the number of inhibitory
and excitatory synapses in the conditioned barrel.
Raddy Ramos (Queens College, CUNY) reported
that inbred mouse strains have a high incidence of
cortical malformations. Surveying 11 inbred strains
and the Allen Brian Atlas revealed that approxi-
mately 30% of animals possessed gross cortical
malformations whereas outbred strains did not.
Friday afternoon began with another series of short
talks moderated by Mary Ann Wilson (Johns
Hopkins University). Mitra Hartmann
(Northwestern University) focused on the mechan-
ical basis of three-dimensional feature extraction.
She argued that animals must integrate across
multiple whiskers and that these computations may
take place in the Interpolaris division of the Spinal
nucleus of V. The animal must account for three
angular positions (horizontal and vertical planes) as
well as torsion (rotation of the whisker), three
moments (twists of the whisker, push of the whisker
in the horizontal and vertical planes), and three
forces (vertical and horizontal translation of the
whisker, axial). Peter Cahusac (University of
Stirling) highlighted the role that metabatropic
glutamate receptors have on processing within the
barrel. These receptors are often located extrasynap-
tically and may play important roles in modulating
overall activity within the barrel cortex.
Barrels XX concluded with another data blitz prior
to the final session on the synaptic plasticity of the
barrel system which was moderated and introduced
by David Kleinfeld (University of California
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San Diego). Dr Kleinfeld highlighted the role that
spike timing dependent plasticity has in sensorimotor
systems and the role that plasticity has in shaping and
maintaining the connections within the barrel
system. Kevin Fox (Cardiff University) highlighted
the role of nitric oxide (NO) in the development and
maintenance of synaptic plasticity within the barrel
cortex. Blocking the synthesis of NO postsynaptically
significantly reduced the induction of long-term
potentiation. In addition, mice where NO produc-
tion has been genetically deleted within the cortex
eliminate both pre- and postsynaptic components of
potentiation. Hui Chen Lu (Baylor University)
focused on the anatomy and physiology of
mGLUR5 knockout mice that have small barrels
and altered staining using cellular (Nissl) and
metabolic (cytochrome oxidase) stains. Experiments
revealed that these animals had a longer critical
period where follicle lesions could still impact barrel
formation. Cortical neurons in knockout mice
displayed more numerous spines on their dendrites
and showed larger amplitude mEPSPs. Finally,
Alison Barth (Carnegie Mellon University)
showed that following one day where just one
whisker was preserved on each side of the face,
there was an increase in spike output for the neurons
in the preserved barrel. Further analysis of these mice
in vitro revealed that the size of the AMPA-mediated
response in the supragranular layers following
stimulation of layer IV was increased and long-term
potentiation could not be evoked in the spared
column. Dr Barth argued that the lack of LTP was
due to the fact that following the deprivation all the
synapses have already been strengthened and thus no
further increases in synaptic strength were possible.
The Barrels meeting remains the oldest satellite
meeting to the Society for Neuroscience annual
meeting. Barrels XX once again highlighted the
diversity of research that is conducted in this model
system for cortical development, anatomy, physiol-
ogy, and behavior.
The Barrels meeting was supported by NSF-Division
of Integrative and Organismal Systems (065052) and
NINDS 1R12NS065167-01 to J.C.B. Barrels XX
was organized by Drs Joshua Brumberg, Randy
Bruno, Mitra Hartmann, Alexis Hattox, David
Kleinfeld, Jochen Staiger, and Mary Ann Wilson.
Special thanks to Kathy Diekmann and Nancy
Steinmetz for logistical support.
4 R. L. Ramos & J. C. Brumberg