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Yu Kai 2010/09/27

Journal Club

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Introduction In sensory cortical areas, neurons are turned to specific stimulus features. In the present paper, the authers investigate the characteristics of the synaptic input that cortical neurons receive to generate their output firing pattern in the visual cortex of mouse.

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The mechanism by which neurons generate signals:

Output as spikes

Input in dendritic synapase

Integration in neuron soma

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Isolation of input from neuron in vivo

They use the approach combining high-speed two-photon imaging with whole-cell patch recordings to identify local sub-threshold calcium signals that correspond to orientation-specific synaptic inputs

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Isolation of input from neuron in vivo

Whole-cell current-clamp recordings of responses todrifting gratings of different orientations. Three trials were superimposed.

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Isolation of input from neuron in vivo:Calcium transient in distal dendrites

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Isolation of input from neuron in vivo:Calcium recordings from five neighbouring dendritic regions

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Isolation of input from neuron in vivo:Exclusive the dendritic NMDA spike

Results: Visually evoked action potentials, subthreshold depolarizations

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Results:Distribution of dendritic hotspots (red dots) to the prefered orientation stimuli

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Results: Orientation perfermance different in the same dentrite

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Conclusion:The results reveal basic insights into the

dendritic organization of sensory inputs to neurons of the visual cortex in vivo.

• Identified discrete dendritic hotspots as synaptic entry sites for specific sensory features

• Afferent sensory inputs with the same orientation preference are widely dispersed over thedendritic tree and do not converge on single dendrites

• Neurons with a highly tuned output signal receive input signals that are heterogeneous

The results support a neuronal integration model involving summation of distributed inputs, rather than models that stress the role of convergent inputs to single dendrites.

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Progress Report

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Verify responsibilities of MGB locus which very close to the injection position

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Injetion Lidocaine into the MGB while continuous recording in A1

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Raster Plot indicate the lidocaine injection cause inversible change on the firing pattern of responses to acoustic stimulation.

Lidocaine Injection

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Corresponding recording before lidocaine injection

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After

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Intracellular Recording of cortical neuron in layer2/3 Before lidocaine into MGB

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After