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Cortex Is Driven by Weak but Synchronously Active Thalamocortical Synapses
Randy M. Bruno* and
Bert Sakmann
Sensory stimuli reach the brain via the thalamocortical projection,a group of axons thought to be among the most powerful in theneocortex. Surprisingly, these axons account for only 15% ofsynapses onto cortical neurons. The thalamocortical pathwaymight thus achieve its effectiveness via high-efficacy thalamocorticalsynapses or via amplification within cortical layer 4. In ratsomatosensory cortex, we measured in vivo the excitatory postsynapticpotential evoked by a single synaptic connection and found thatthalamocortical synapses have low efficacy. Convergent inputs,however, are both numerous and synchronous, and intracorticalamplification is not required. Our results suggest a mechanismof cortical activation by which thalamic input alone can drivecortex.
Department of Cell Physiology, Max Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany.
* To whom correspondence should be addressed. E-mail: bruno{at}mpimf-heidelberg.mpg.de
Spatial Organization of Neuronal Population Responses in Layer 2/3 of Rat Barrel Cortex.
J. N. D. Kerr, C. P. J. de Kock, D. S. Greenberg, R. M. Bruno, B. Sakmann, and F. Helmchen (2007)
J. Neurosci.
27, 13316-13328
|Abstract »|Full Text »|PDF »
Thalamocortical Conduction Times and Stimulus-Evoked Responses in the Rat Whisker-to-Barrel System.
D. J. Simons, G. E. Carvell, H. T. Kyriazi, and R. M. Bruno (2007)
J Neurophysiol
98, 2842-2847
|Abstract »|Full Text »|PDF »
Modeling a layer 4-to-layer 2/3 module of a single column in rat neocortex: Interweaving in vitro and in vivo experimental observations.
L. Sarid, R. Bruno, B. Sakmann, I. Segev, and D. Feldmeyer (2007)
PNAS
104, 16353-16358
|Abstract »|Full Text »|PDF »
A Biologically Realistic Model of Contrast Invariant Orientation Tuning by Thalamocortical Synaptic Depression.
Y. Banitt, K. A. C. Martin, and I. Segev (2007)
J. Neurosci.
27, 10230-10239
|Abstract »|Full Text »|PDF »
Interspike Interval Analysis of Retinal Ganglion Cell Receptive Fields.
D. L. Rathbun, H. J. Alitto, T. G. Weyand, and W. M. Usrey (2007)
J Neurophysiol
98, 911-919
|Abstract »|Full Text »|PDF »
Enhancement of Visual Responsiveness by Spontaneous Local Network Activity In Vivo.
B. Haider, A. Duque, A. R. Hasenstaub, Y. Yu, and D. A. McCormick (2007)
J Neurophysiol
97, 4186-4202
|Abstract »|Full Text »|PDF »
Layer- and cell-type-specific suprathreshold stimulus representation in rat primary somatosensory cortex.
C. P. J. de Kock, R. M. Bruno, H. Spors, and B. Sakmann (2007)
J. Physiol.
581, 139-154
|Abstract »|Full Text »|PDF »
Thalamocortical Up States: Differential Effects of Intrinsic and Extrinsic Cortical Inputs on Persistent Activity.
Cranial Visceral Afferent Pathways through the Nucleus of the Solitary Tract to Caudal Ventrolateral Medulla or Paraventricular Hypothalamus: Target-Specific Synaptic Reliability and Convergence Patterns..
T. W. Bailey, S. M. Hermes, M. C. Andresen, and S. A. Aicher (2006)
J. Neurosci.
26, 11893-11902
|Abstract »|Full Text »|PDF »
Efficacy and connectivity of intracolumnar pairs of layer 2/3 pyramidal cells in the barrel cortex of juvenile rats.
15% of synapses onto cortical neurons. The thalamocortical pathway might thus achieve its effectiveness via high-efficacy thalamocortical synapses or via amplification within cortical layer 4. In rat somatosensory cortex, we measured in vivo the excitatory postsynaptic potential evoked by a single synaptic connection and found that thalamocortical synapses have low efficacy. Convergent inputs, however, are both numerous and synchronous, and intracortical amplification is not required. Our results suggest a mechanism of cortical activation by which thalamic input alone can drive cortex. 
