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Investigating Object Representations in the Macaque Dorsal Visual Stream Using Single-unit Recordings
Published on: August 1, 2018
Development of temporal response properties and contrast sensitivity of V1 and V2 neurons in macaque monkeys
1University of Houston, College of Optometry, 505 J. Davis Armistead Bldg., Houston, TX 77204-2020, USA.
Insights
Infant monkey visual cortex (V1 and V2) neurons show immature temporal vision and contrast sensitivity. Maturation of these visual areas limits early visual development in infants.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Visual Neuroscience
Background:
- Infant temporal contrast sensitivity is lower than adult levels.
- The specific neural structures limiting early visual maturation remain unclear.
Purpose of the Study:
- Investigate neural responses in infant monkey primary visual cortex (V1) and visual area 2 (V2).
- Examine neuronal responses to temporal modulation and varying stimulus contrasts during early development.
Main Methods:
- Recorded neuronal activity in V1 and V2 of infant and adult monkeys.
- Utilized temporally modulated grating stimuli across a range of contrasts.
- Analyzed temporal frequency tuning, optimal temporal frequency, temporal resolution, onset latency, and contrast thresholds.
Main Results:
- V1 and V2 neurons exhibited band-pass temporal tuning from 2 weeks of age.
- Infant V1 neurons showed lower optimal temporal frequency and resolution at 2-4 weeks compared to adults.
- V2 neurons in 8-week-old monkeys had reduced temporal resolution compared to adults.
- Contrast thresholds were higher in younger infants (2-4 weeks) but normalized by 8 weeks.
- Higher onset latency was observed in infant V1 and V2 neurons.
Conclusions:
- Early visual development, including temporal vision and contrast sensitivity, is influenced by precortical structures.
- Immature neural properties unique to V1 and V2 also limit the maturation of temporal vision in infants.
- Visual cortex maturation plays a critical role in achieving adult-like visual performance.
Abstract:
The temporal contrast sensitivity of human infants is reduced compared to that of adults. It is not known which neural structures of our visual brain sets limits on the early maturation of temporal vision. In this study we investigated how individual neurons in the primary visual cortex (V1) and visual area 2 (V2) of infant monkeys respond to temporal modulation of spatially optimized grating stimuli and a range of stimulus contrasts. As early as 2 wk of age, V1 and V2 neurons exhibited band-pass temporal frequency tuning. However, the optimal temporal frequency and temporal resolution of V1 neurons were much lower in 2- and 4-wk-old infants than in 8-wk-old infants or adults. V2 neurons of 8-wk-old monkeys had significantly lower optimal temporal frequencies and resolutions than those of adults. Onset latency was longer in V1 at 2 and 4 wk of age and was slower in V2 even at 8 wk of age than in adults. Contrast threshold of V1 and V2 neurons was substantially higher in 2- and 4-wk-old infants but became adultlike by 8 wk of age. For the first 4 wk of life, responses to high-contrast stimuli saturated more readily in V2. The present results suggest that although the early development of temporal vision and contrast sensitivity may largely depend on the functional maturation of precortical structures, it is also likely to be limited by immaturities that are unique to V1 and V2.
