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Somatosensory and Motor Research

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Barrels XIX Meeting Report

Raddy L. Ramos

; Joshua C. Brumberg

Department of Psychology, Queens College, CUNY, NY, USA

First Published on: 01 September 2007

To cite this Article: Ramos, Raddy L. and Brumberg, Joshua C. (2007) 'Barrels XIX

Meeting Report', Somatosensory and Motor Research, 24:3, 135 - 138

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Somatosensory and Motor Research, September 2007; 24(3): 135–138

Barrels XIX Meeting Report

RADDY L. RAMOS & JOSHUA C. BRUMBERG

Department of Psychology, Queens College, CUNY, NY, USA

The 19th annual Barrels Meeting (Barrels XIX)

was hosted by the Neuroscience Institute at

the Morehouse School of Medicine in Atlanta,

Georgia on 12th and 13th of October 2006. The

meeting brought together over 125 researchers from

ten different countries to discuss the anatomy,

physiology, and behavior of the rodent whisker-to-

barrel pathway as well as its associated neuronal

structures.

The meeting began with a session focused on

the neuronal activity patterns evoked by whisker

deflections. Dr Mathew Diamond (SISSA, Trieste,

Italy) focused on the effect that temporal noise had

on action potential discharges in the barrel cortex.

Noise was defined in the temporal domain such that

the overall stimulation rate was fixed at a specific

rate, for example, 10 or 20 Hz but the interval

between stimuli was varied accordingly. It was found

that as the noise increased there was less adaptation

to the stimulus presentation and the magnitude and

temporal precision of the cortical response increased.

It was suggested that the noise in the stimulus may

play an adaptive role in setting the gain of the

whisker-to-barrel system with low frequency noise

resulting in low velocity sensitivity whereas high

frequency noise makes the system more sensitive to

high velocity stimuli. Dr Daniel Barth (University of

Colorado) followed with a talk that demonstrated

the existence of fast oscillations within the barrel

system and that they served as coincident detectors

for inputs from multiple whiskers. Similar to classic

single unit studies conducted by Daniel Simons

and colleagues, field potential recordings show

suppressive effects between adjacent whiskers which

act to sharpen the temporal window in which

coincidence detection can occur. Interestingly,

there were no differences in summation between

within arc vs. within row interactions suggesting that

the barrel cortex may function as a two-dimensional

integrative array. The session was concluded by

Dr Mitra Hartmann (Northwestern University) who

asked the question, what aspect(s) of tactile stimuli

is/are encoded by the whisker? Using a combination

of robotic, computational, and neurophysiological

approaches Dr Hartmann argues that moment (often

called torque) and the rate of change of moment are

crucial for three-dimensional feature extraction of an

object by a rodent’s whiskers.

The past year saw the passing of Peter Land

(University of Pittsburgh) a respected member of the

Barrels community. Daniel Simons (University of

Pittsburgh) a longtime friend and collaborator

reminded the community of Peter Land’s research

accomplishments with special emphasis on his work

in studying the development of the barrel system.

Peter will be remembered fondly for his enthusiasm

not only for scientific research but for experiencing

life to its fullest extent.

A series of short talks highlighted the diversity of

responses seen within the barrel system in vivo

following whisker deflections. Vincent Jacob

(CNRS, Gif-sur-Yvette, France) presented results

from intracellular in vivo recordings from barrel

cortex while simultaneously stimulating up to 25

whiskers on the contralateral mystacial pad. Using a

sparse noise stimuli, Jacob and his colleagues were

able to construct spatiotemporal receptive fields for

each neuron and found that most neurons had multi-

whisker receptive fields and were sensitive to the

temporal ordering of whisker contacts. Does a single

neuron’s firing have an effect on sensory

processing? To address this question, Arthur

Howeling and Michael Brecht (Erasmus, the

Correspondence: J. C. Brumberg, Department of Psychology, Queens College, CUNNY, 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 2007 Informa UK Ltd.

DOI: 10.1080/08990220701538562

Downloaded By: [University of Connecticut] At: 01:53 26 January 2008

Netherlands) used a head-fixed awake-behaving

preparation to show that in vivo juxtacellular micro-

stimulation of individual barrel neurons could elicit

a sensation measure via tongue lick responses.

Soo-Hyun Lee (University of Pittsburgh) showed

that activation of primary motor cortex (M1) can

result in expression of sensory-evoked receptive fields

in antidromically activated corticothalamic neurons

that under control conditions did not display

suprathreshold responses. Finally, Shubo

Chakrabarti (Pennsylvania State University College

of Medicine) demonstrated that primary motor

cortex neurons, especially those in the deeper layer,

demonstrate short-latency responses to whisker

stimulation. Inactivation of S1 and S2 led to a

decrease in the magnitude of the M1 response

suggesting that these areas provide feedforward

inputs to M1.

In another series of short talks, the growing

emphasis on the intrinsic biomechanics of the

vibrissae was highlighted. Jason Wolfe (University

of California San Diego) showed that during active

whisking in air, whiskers demonstrate different

resonances that are not due to air currents or head

motion. Furthermore, during active whisking

of textured surfaces (sandpaper) it was seen that

stick-slip whisker events were observed, though the

nature of the frequency of the whisker responses did

not vary as a function of the roughness of the texture.

These results suggest that during whisking in air vs.

contact with stimuli, the whisker is in an undamped

vs. damped regime, respectively. Jason Ritt

(Massachusetts Institute of Technology) using

high speed videography, further demonstrated

the existence of stick-slip events when whiskers

contacted a surface. The result of such events was a

‘‘ringing’’ of the whisker whose frequency was

proportional to the reciprocal of the whisker length

squared. These observations suggested that the

conventional stimuli used to probe receptive fields

in anesthetized preparations have significantly lower

velocities than is observed during active whisking

epochs. Dan Hill (University of California

San Diego) showed that a sequence of extrinsic and

then intrinsic muscles govern the whisking cycle and

that there are three distinct phases of muscle activity.

The first phase is characterized by retraction and is

mediated by the extrinsic muscles (M. nasolabialis

and M. maxillolabialis). The second and third phases

are characterized by protractions and are governed

by the extrinsic muscle M. nasalis followed by

the intrinsic muscles. Tony Prescott (University

of Sheffield, UK) showed that rats can perform

asymmetric whisking in cases where one mystacial

pad contacts an object and remains relatively still

while the whiskers on the opposite side of the

face continue to move. Using their videographic/

behavioral results, they were able to construct

a robotic rodent (whiskerbot) that could whisk

and orientate to objects. Carl Peterson

(Ecole Polytechnique Federale de Lausanne,

Switzerland) using a combination of in vivo whole-

cell recordings and voltage sensitive dye imaging

showed that single whisker deflections can result in

the activation of the large majority of the cortical

plate. Activation was first observed in S1 followed

at short latency by responses in M1 which may

drive future whisker movements or head orienting

responses. Finally, Venkatesh Gopal (Northwestern

University) detailed the construction of the

‘‘Whole Rat Catalog’’, a complete three-dimensional

reconstruction of the rat face including the position,

shapes, and orientations of all whiskers. Such

a database was offered as a way of understanding

the movement and orientation of the whiskers and

head during behaviors involving the whiskers

or olfactory stimuli. The meeting continued with

a poster session whose abstracts follow this report.

The second day of Barrels XIX began with a talk

by Steve Hsiao ( Johns Hopkins University) provid-

ing data from single unit recording studies in awake,

behaving monkeys. Within the periphery, sensory

afferents do not convey any information about

stimulus orientation. In contrast, S1 neurons were

shown to be well tuned for orientation and data from

neural recordings were well matched to identified

psychometric thresholds. In S2, three maps exist with

neurons having different receptive field properties

(untuned excitatory RFs, untuned inhibitory

RFs, and orientation tuned RFs). These different

RF types show changes in firing rates in response to

changes in hand position which may be important in

object perception.

Following Dr Hsiao’s talk there was another series

of short talks focusing on data derived from in vivo

studies. First to present was Tatiana Bezdudnaya

(University of Maryland) who provided new data

from single unit recordings from the lateral

dorsal nucleus (LD) of the thalamus. In urethane-

anesthetized rats, it was observed that whisker

stimulation resulted in short-latency excitatory

responses suggestive of direct input from peripheral

afferents. Consistent with this observation, electrical

stimulation of nucleus interpolaris resulted in

short-latency excitation of LD units. Interestingly,

electrical stimulation of barrel cortex resulted in

both antidromic and orthodromic responses, sug-

gesting reciprocal connections from LD to barrel

cortex. Randy Bruno (Max Planck Institute for

Medical Research) presented data from recordings

from pairs of connected thalamic and barrel neurons

in vivo. Whole-cell recordings from barrel

neurons and cell-attached recordings from thalamic

neurons provided unequivocal confirmation of

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

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connected pairs and revealed that single thalamocor-

tical (TC) impulses result in very weak excitation of

barrel neurons (51mV). These data emphasize the

importance that synchronous firing of many TC

neurons converging onto individual barrel neurons

has on the excitation of barrel cortex.

Robert Sachdev ( Yale University) presented in vivo

intracellular recordings from barrel neurons during

spontaneous membrane potential fluctuations

(up–down states). Interestingly, the up-state was

found to be associated with decreased responsiveness

to whisker stimulation and appears to be mediated by

increased inhibition. Whisker stimulation during

down-states often resulted in transitions to up-states

suggesting that peripheral inputs can trigger

widespread excitation of barrel circuits. Jason Kerr

(Max Planck Institute for Medical Research)

demonstrated the response properties of networks

of barrel neurons to whisker stimulation with

2-photon calcium imaging. Neurons responding to

stimulation onset, offset, or both were detected as

well as network-level response features. Whisker

stimulation resulted in greater spatial correlations

in network activity compared to spontaneous firing.

With the same imaging preparation, David

Greenberg (Max Planck Institute for Medical

Research) used reverse correlation and information

theory to evaluate the predictive strength of detecting

whisker stimulation onset. Near perfect detection of

stimuli was achieved when data from 175 to 200

simultaneously imaged neurons were included in

analyses. Gaute Einevoll (Norwegian University of

the Life Sciences) described novel quantitative

methods to extract network-level connections

between cortical lamina from data acquired with

linear electrode arrays. Extracting low frequency

local field potentials representing synaptic inputs and

high frequency signals from spiking neurons, this

novel method (Laminar Population Analysis) can

demonstrate the sequential spread of excitation from

granular to supragranular layers and can be used to

detect novel connection patterns. Maria Popescu

(Vanderbilt University) presented single unit data

from rats following unilateral or bilateral whisker

trimming. Bilateral deprivation resulted in a decrease

in spontaneous and evoked responses in both

barrel and septal columns. In contrast, unilateral

deprivation (UD) resulted only in changes in and

above barrels, while septal neurons remained

unchanged.

Moving to anatomical and in vitro studies in the

afternoon, Julian Broser (Max Planck Institute

for Medical Research) demonstrated axonal

reorganization made by layer 2/3 barrel neurons

following whisker trimming. Whisker trimming of

rows A–C was combined with injection of a lentiviral

vector encoding GFP into the D2 barrel which

revealed a significant reduction in the number of

axons projecting toward C row barrels. Axonal

reorganization was restricted to axons of

supragranular neurons. Alexis Hattox (Brandies

University) identified layer 5 barrel cortex neurons

which projected to the striatum, the contralateral

cortex, the thalamus, or trigeminal nuclei following

retrograde labeling and targeted these neurons for

whole-cell recordings in vitro. Neurons with callosal

and striatal projections were found to display similar

intrinsic electrophysiological properties including

strong spike frequency adaptation. In contrast, layer

5 neurons with thalamic as well as trigeminal

projections showed little adaptation. Microarray

analysis of layer 5 neurons revealed differential

expression of several genes including potassium

channels which may underlie the physiological

phenotype of each cell type. Raddy Ramos

(Queens College, CUNY) presented data from

in vitro, whole-cell recordings of identified callosal

neurons in layer 2/3. Retrogradely labeled callosal

neurons displayed a ‘‘regular-spiking’’ phenotype

and had pyramidal cell morphologies including

spiny dendrites. In order to reveal the axonal

projections of callosal neurons, GFP was expressed

in layer 2/3 neurons by electroporation in utero.

Analysis of labeled axons revealed that layer 2/3

callosal neurons preferentially target layers 1–3 and

5/6 while avoiding layer 4.

The meeting was concluded with two talks which

utilized imaging techniques to assay neuronal

structure and function. Wen-Biao Gan (New York

University) discussed the growth and elimination of

dendritic spines as well as the effect of sensory

deprivation on these processes. During the first

postnatal month, dendritic development in barrel

cortex is characterized preferentially by spine

elimination rather than growth. Sensory deprivation

via whisker trimming during this period results in a

reduction in the number of spines eliminated and

subsequent regrowth of whiskers accelerates spine

elimination. The second talk was by Fritjof

Helmchen (University of Zurich), who presented

advances in 2-photon microscopy for use in imaging

large three-dimensional neuronal networks in vivo

during the presentation of controlled whisker stimuli.

Piezo-electric devices were used to move objectives

along predetermined trajectories in order to

image from up to 400 cells including neurons and

astrocytes. Alternatively, objectives could be moved

to image selected cells found along various depths

and spatial locations.

Barrels XIX emphasized the inter-disciplinary

nature of the field with presentations using a whole

host of modern molecular, cellular, physiological,

and imaging techniques to probe the structure and

function of the barrel model system.

Barrels XIX Meeting Report 137

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Acknowledgements

Thanks to Cathy Woodley and Dr Peter MacLeish

for their assistance at the Morehouse School of

Medicine. Ms Kathy Diekmann was instrumental in

putting the meeting together and Drs Randy Bruno,

Mitra Hartmann, and Jochen Staiger assisted in

planning the meeting. The meeting was supported

with generous support from the National Science

Foundation, Division of Integrative and Organismal

Biology.

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