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Achromatic temporal-frequency responses of human lateral geniculate nucleus and primary visual cortex
Ali Bayram1, Esin Karahan2, Başar Bilgiç3
1Istanbul University, Institute of Experimental Medicine, Department of Neuroscience, Istanbul, Turkey; Istanbul University, Hulusi Behcet Life Sciences Research Laboratory, Istanbul, Turkey.
Vision Research
|September 11, 2016
Summary
The human visual system processes temporal frequencies differently in the lateral geniculate nucleus (LGN) and primary visual cortex (V1). V1 shows a low-pass filter effect, with responses peaking at 8-12Hz and declining significantly above 14Hz.
Area of Science:
- Neuroscience
- Visual Perception
- Human Physiology
Background:
- Sensory system sensitivity to temporal environmental changes is crucial for perception.
- Understanding the early visual system's temporal processing is key to visual perception research.
Purpose of the Study:
- Investigate the human early visual system's dependence on temporal frequency of visual input.
- Characterize the blood oxygen level-dependent (BOLD) responses in the lateral geniculate nucleus (LGN) and primary visual cortex (V1) across a range of temporal frequencies.
Main Methods:
- Functional magnetic resonance imaging (fMRI) was used to measure BOLD responses.
- Investigated a wide temporal frequency range (6-46Hz) with fine sampling (13 frequencies).
- Subject-specific functional-anatomic regions of interest (ROIs) were derived and analyzed for LGN and V1, with V1 further analyzed by eccentricity sectors.
Main Results:
- LGN responses showed fluctuations with a non-significant decreasing trend as frequency increased.
- V1 responses exhibited fluctuations with a global maximum between 8-12Hz, followed by a significant decrease above 14Hz.
- This low-pass filtering effect in V1 was consistent across central and peripheral vision, suggesting V1 circuitry or extrastriate projections are involved.
Conclusions:
- The primary visual cortex (V1) acts as a low-pass filter for visual input, emerging from its internal circuitry or extrastriate connections.
- High correlation between LGN and V1 BOLD responses supports the concept of oscillatory tuning in thalamo-cortical interactions.
- These findings provide insights into the temporal dynamics of early visual processing and thalamo-cortical communication.
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