The Bernstein Center for Computational Neuroscience Freiburg

Announcement for the next
BCCN Seminar
Randy M. Bruno, Ph.D.
Department of Cell Physiology
Max Planck Institute for Medical Research
Strengths & Weaknesses of Thalamocortical Synapses:
A model for communication between brain regions

Thursday, May 3rd, 2007
Lecture Hall (ground floor)
BCCN building
Hansastraße 9A
79104 Freiburg
A century of neuroscience research has identified many of the major functions of the mammalian brainís various regions and the gross anatomical pathways interconnecting them. Nevertheless, their precise architecture is largely unknown at the level of synaptic connections between individual processing units (neurons). I have been examining in vivo neural networks in the context of the connectivity between two main brain regions: thalamus and cortex. Sensory stimuli from our environment reach the cortex via the thalamocortical projection, a group of axons thought to be among the most powerful in the brain. Surprisingly, these axons account for only ~15% of synapses onto cortical neurons. The thalamocortical pathway might thus achieve its effectiveness via high-efficacy thalamocortical synapses or via amplification within the main cortical input layer. I recently 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. These results suggest a mechanism of cortical activation by which thalamic input alone can drive cortex. Combined with previous observations of strong feedforward inhibition and dense intracortical recurrency, our results also suggest a specific function for intracortical connections.
The talk is open to the public. Guests are cordially invited!