Bilateral and unilateral odor processing and odor perception

Abstract

Imagine smelling a novel perfume with only one nostril and then smelling it again with the other nostril. Clearly, you can tell that it is the same perfume both times. This simple experiment demonstrates that odor information is shared across both hemispheres to enable perceptual unity. In many sensory systems, perceptual unity is believed to be mediated by inter-hemispheric connections between iso-functional cortical regions. However, in the olfactory system, the underlying neural mechanisms that enable this coordination are unclear because the two olfactory cortices are not topographically organized and do not seem to have homotypic inter-hemispheric mapping. This review presents recent advances in determining which aspects of odor information are processed unilaterally or bilaterally, and how odor information is shared across the two hemispheres. We argue that understanding the mechanisms of inter-hemispheric coordination can provide valuable insights that are hard to achieve when focusing on one hemisphere alone. I n the early 1940s, patients suffering from severe untreatable epileptic seizures underwent a pioneering operation in which their corpus callosum was severed. While this mitigated the epilepsy syndromes, it generated strange phenomena: each hemisphere seemed to have its own separate perception, concepts, and even actions. When such split-brain patients were shown an image of an object in their left visual field, they could not vocally name what they had seen. This is because information about the image seen in the left visual field is sent only to the right side of the brain, while the speech-control center is usually on the left side of the brain. Nonetheless, patients could pick up the correct object with their left hand because it is controlled by the right hemisphere 1. Some of the surgery-induced deficits improved over time, but they illustrate one important principle: the fibers that interconnect the hemispheres are responsible for transferring information from one side to the other. These connecting fibers may be required to achieve perceptual unity, at least in some sensory modalities. But how is perceptual unity achieved? There are several possible ways to achieve perceptual unity in the healthy brain. One way is to ensure that sensory information is transmitted to both hemispheres directly from the sensory organs. This is how auditory information is unified across hemispheres: information from both ears converges to the left and the right Superior Olivary

Towards Deciphering the Fetal Foundation of Normal Cognition and Cognitive Symptoms From Sulcation of the Cortex

“…Some folding patterns are preserved across species, complex patterns in larger brains likely emerging from simplified patterns in smaller brains (Borrell and Reillo, 2012 ). The heritability of cortical folding is estimated between 20 and 50% (Le Guen et al, 2018 ; Pizzagalli et al, 2020 ), supporting a major effects of early environmental factors on sulcation and cognition, including alcohol exposure (De Guio et al, 2014 ), intrauterine growth restriction (Dubois et al, 2008a ) or twin pregnancy (Amiez et al, 2018 ).…”

Bilateral Alignment of Receptive Fields in the Olfactory Cortex

“…Recent evidence suggests 78 that mitral cells in the OB may have matched responses through 79 organized feedback projections from the anterior olfactory nucleus 80 (AON) par externa (Grobman et al, 2018;Yan et al, 2008). A cortical 81 neuron may then be able to inherit the matched response from mitral 82 cells (Dalal et al, 2020), but a direct evaluation of cortical matching is 83 lacking 84…”

Radial symmetry molding skull roundness: a human fetal MR study

“…A narrower human nose could have allowed an increased sensitivity to odorants, improved the accuracy of directional orientation, with greater survival possibilities in the wild environment. The existence of two symmetrical nostrils suggests that humans might use bilateral sampling to extract information about the location of a speci c odorant source 32,33 . On the other side, the development of the visual perception allowed humans to gather precious information from the environment concerning threat and safety, successful foraging and sexual opportunity 34 .…”