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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

RADDY L. RAMOS, & JOSHUA C. BRUMBERG

Department of Psychology, Queens College, CUNY, New York, USA

(Received 22 22 22; revised 22 22 22; accepted 22 22 22)

Abstract

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: Joshua.brumberg@qc.cuny.edu

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

100

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

105

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

110

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

115

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,

120

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.

125

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

130

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.

135

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

140

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

145

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

150

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

155

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

160

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

165

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

170

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

175

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.

180

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

185

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

190

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

195

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-

200

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

205

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

210

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

215

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

220

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

225

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

(PLCB

) has on the development of the barrel

230

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

235

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

240

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-

245

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

250

series of short talks moderated by Mary Ann Wilson

(Johns Hopkins University). Amy Nakashima

(University of Calgary) showed that Zn

2þ

expression

within the barrel cortex was influenced by the

sensory environment. Rats in deprived (C-row

255

trimmed) conditions showed elevated Zn

2þ

levels

in the deprived barrels. Interestingly, animals reared

in an enriched environment for at least 1 week also

showed an increase in Zn

2þ

staining. Malgorzata

Kossut (Nencki Institute for Experimental Biology),

260

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

265

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-

270

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

275

(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

280

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

285

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-

290

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

295

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

300

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

305

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

310

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

315

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

320

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

325

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

330

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

335

system for cortical development, anatomy, physiol-

ogy, and behavior.

Acknowledgements

The Barrels meeting was supported by NSF-Division

of Integrative and Organismal Systems (065052) and

340

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

345

Steinmetz for logistical support.

4 R. L. Ramos & J. C. Brumberg