Cortex is driven by weak but synchronously active thalamocortical synapses.
Sensory stimuli reach the brain via the thalamocortical projection, a group of axons thought to be among the most powerful in the neocortex. Surprisingly, these axons account for only approximately 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.
Bruno
Randy M
RM
Department of Cell Physiology, Max Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany. bruno@mpimf-heidelberg.mpg.de
Sakmann
Bert
B
D000200:Action Potentials; D000818:Animals; D001369:Axons / Q000502:physiology; D003712:Dendrites / Q000502:physiology; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials; D008564:Membrane Potentials; D009434:Neural Pathways; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013003:Somatosensory Cortex / Q000166:cytology / Q000502:physiology*; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission; D013788:Thalamus / Q000166:cytology / Q000502:physiology*; D014738:Vibrissae / Q000294:innervation / Q000502:physiology