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Orientation selectivity without orientation maps in visual cortex of a highly visual mammal
Stephen D Van Hooser1, J Alexander F Heimel, Sooyoung Chung
1Brandeis University, Waltham, Massachusetts 02454, USA. vanhoosr@brandeis.edu
Summary
Orientation maps, common in mammals, are absent in gray squirrels' primary visual cortex (V1). This suggests that orderly cortical maps are not universal, even with robust neuronal orientation tuning.
Area of Science:
- Neuroscience
- Comparative Anatomy
- Visual System Research
Background:
- Mammalian neocortex exhibits organized neuronal structures, like orientation maps in the primary visual cortex (V1).
- Orientation maps, where neurons respond to specific stimulus orientations, are prevalent in many mammals but notably absent in rodents and lagomorphs.
- Previous studies suggested rodent V1 organization might be limited by factors like low visual acuity or small V1 size.
Purpose of the Study:
- Investigate the presence of orientation maps in a highly visual rodent, the gray squirrel, to understand the variability of cortical organization.
- Determine if the absence of orientation maps in rodents is linked to specific visual processing capabilities or V1 characteristics.
- Explore the relationship between orientation maps, neuronal orientation tuning, and columnar organization.
Main Methods:
- Utilized intrinsic signal optical imaging to visualize neural activity patterns in the gray squirrel's V1.
- Performed single-cell recordings to analyze the orientation tuning properties of individual neurons.
- Conducted vertical electrode penetrations to assess columnar organization and local variations in orientation preference.
Main Results:
- Found no evidence of a systematic orientation map in the gray squirrel's V1.
- Confirmed robust orientation tuning in individual neurons, which remained effective regardless of stimulus contrast.
- Observed minimal evidence for columnar organization of orientation-selective neurons or local anisotropy in orientation preferences.
Conclusions:
- The absence of orientation maps in the gray squirrel suggests that their formation relies on mechanisms not present in rodents.
- Orientation maps are not essential for achieving precise orientation tuning or contrast invariance in V1.
- Orderly, columnar arrangement of functional properties is not a universal feature of mammalian cortical architecture.