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The Second Spiking Threshold: Dynamics of Laminar Network Spiking in the Visual Cortex
Lars E Forsberg1, Lars H Bonde2, Michael A Harvey1
1Brain Research, Department of Neuroscience, Karolinska Institute Solna, Sweden.
Frontiers in Systems Neuroscience
|September 2, 2016
Summary
Neurons possess a second threshold distinguishing spontaneous from visually evoked spiking across all cortical layers. This network property clarifies transitions between neural activity states in response to visual stimuli.
Area of Science:
- Neuroscience
- Computational Neuroscience
- Visual System Research
Background:
- Neurons exhibit a firing threshold between silence and spiking.
- A recently identified second threshold separates spontaneous from evoked spiking in visual cortex granular layers.
Purpose of the Study:
- To investigate the presence and characteristics of this second threshold beyond the granular layer.
- To analyze the dynamics of transitions between neural spiking states in response to visual stimuli.
Main Methods:
- Electrophysiological recordings in ferret visual cortex (areas 17 and 18).
- Analysis of neural activity in response to stationary, moving, and transient visual stimuli.
- State-space analysis of neural trajectories during spontaneous and evoked spiking.
Main Results:
- The second threshold exists in all layers and zones of areas 17 and 18, indicating it's a network-level property.
- Spontaneous spiking trajectories are slow and variable, while evoked spiking is fast and directed.
- Visual transients, regardless of speed or smoothness, effectively drive transitions from spontaneous to evoked states.
- Evoked states explore a uniform state space and return to the spontaneous state, characteristic of a mono-stable system.
Conclusions:
- The second threshold is a fundamental network property in the visual cortex, distinguishing distinct spiking states.
- Neural dynamics demonstrate a clear distinction between spontaneous and stimulus-evoked activity.
- Visual stimuli reliably evoke a consistent type of neural response, regardless of stimulus presentation details.
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