Orientation processing without orientation maps in the pigeon analogue to the primary visual cortex.
In most mammalian brains, orientation selective neurons of the primary visual cortex are clustered into processing arrays that align vertically to the surface, such that orientation preference is varied systematically in a pinwheel-like arrangement. However in rodents, particularly the highly visual squirrel, no such clustering has been found despite clear orientation selectivity at the single cell level, thereby suggesting that extensive spatial clustering of similarly selective units is not necessary for basic visual capabilities.
In this study, we evaluated the functional organization in the visual wulst of the pigeon, an avian model known to depend heavily on its visual abilities. The pigeon visual wulst is widely assumed to be functionally analogous to the mammalian primary visual cortex, mainly due to its input connectivity to the geniculate nucleus in the thalamofugal pathway. However, further details as to its specific functional role, including its functional architecture for orientation processing is virtually unknown.
Using voltage sensitive dye imaging and electrophysiology, we examined neuronal population activity evoked by drifting gratings of various spatiotemporal frequencies and orientations covering a large portion of the contralateral visual field (~120°x80°).
Here we report that these large stimuli evoked an activation that first emerged from a local region ~25ms after stimulus onset. Local emergence was followed by a rapid spread of activity that covered the whole visual wulst, peaking at ~200ms before rapidly adapting to near-baseline levels (after ~600ms) despite ongoing visual input. We were able to distinguish two different regions; a local, central input region that was sensitive to stimulus duration, and a surround region that showed delayed suppression independent of stimulus duration.
We did not detect any clustering of orientation selective units into regular and distinct orientation domains with particular orientation preferences, but instead found a dominant representation of the vertical orientation.
In conclusion, our results show that wulst processing of oriented stimuli differs from that in the striate visual cortex. In response to a large stimulus, we observed the local emergence, followed by brisk spread and rapid adaptation of activity. This argues for a local input area via which incoming information is distributed to the remainder of the visual wulst, while co-activating strong suppressive mechanisms. Further, the lack of orientation maps in the pigeon reinforces the idea that similar-preference clustering may not be crucial to orientation processing. Finally, we suggest that the dominance of the vertical orientation can be a functional adaptation to the specific visual demands of flight.
Conference:
Computational and systems
neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009.
Presentation Type:
Poster Presentation
Topic:
Poster Presentations
Citation:
(2009). Orientation processing without orientation maps in the pigeon analogue to the primary visual cortex..
Front. Syst. Neurosci.
Conference Abstract:
Computational and systems
neuroscience 2009.
doi: 10.3389/conf.neuro.06.2009.03.051
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Received:
30 Jan 2009;
Published Online:
30 Jan 2009.