Early Auditory Processing in Area V5/MT+ of the Congenitally Blind Brain

162

122

The principles that guide large-scale cortical reorganization remain unclear. In the blind, several visual regions preserve their task specificity; ventral visual areas, for example, become engaged in auditory and tactile object-recognition tasks. It remains open whether task-specific reorganization is unique to the visual cortex or, alternatively, whether this kind of plasticity is a general principle applying to other cortical areas. Auditory areas can become recruited for visual and tactile input in the deaf. Although nonhuman data suggest that this reorganization might be task specific, human evidence has been lacking. Here we enrolled 15 deaf and 15 hearing adults into an functional MRI experiment during which they discriminated between temporally complex sequences of stimuli (rhythms). Both deaf and hearing subjects performed the task visually, in the central visual field. In addition, hearing subjects performed the same task in the auditory modality. We found that the visual task robustly activated the auditory cortex in deaf subjects, peaking in the posterior–lateral part of high-level auditory areas. This activation pattern was strikingly similar to the pattern found in hearing subjects performing the auditory version of the task. Although performing the visual task in deaf subjects induced an increase in functional connectivity between the auditory cortex and the dorsal visual cortex, no such effect was found in hearing subjects. We conclude that in deaf humans the high-level auditory cortex switches its input modality from sound to vision but preserves its task-specific activation pattern independent of input modality. Task-specific reorganization thus might be a general principle that guides cortical plasticity in the brain.

Section: Discussionmentioning

confidence: 91%

Task-specific reorganization of the auditory cortex in deaf humans

Bola

Zimmermann

Mostowski

et al. 2017

162

122

“…It would also be interesting to examine the anatomy and physiology of neurons in the thalamus and somatosensory cortex in Cdx1-Cre;Fz3 CKO/− mice to explore the fate of territories that normally process somatosensory information from the trunk and limbs. One might anticipate that there would be a large scale remapping of these territories analogous to the remapping of visual cortex in humans or animals that are congenitally blind (33)(34)(35).…”

Section: Discussionmentioning

confidence: 99%

Frizzled3 is required for the development of multiple axon tracts in the mouse central nervous system

Hua¹,

Jeon

Caterina

et al. 2014

Targeted mutation of the Frizzled3 (Fz3) gene in mice has been shown to disrupt the growth and guidance of a subset of peripheral and central axons. Here we used conditional deletion of Fz3 to explore the forebrain territories in which Fz3 action is required for the development of the anterior commissure and the corticothalamic, corticospinal, and thalamocortical tracts. Experiments with regionspecific deletion of Fz3 using a variety of Cre lines show that proper routing of corticothalamic and thalamocortical axons in the internal capsule requires Fz3 expression in the ventral telencephalon. The pattern of defects among forebrain axon tracts that are induced by conditional deletion of Fz3 conforms closely to the pattern previously observed with analogous conditional deletion of Celsr3, implying a close mechanistic link between Fz3 and Celsr3 in axon guidance. We further found that several central nervous system axon tracts require Fz3 function as early as embryonic day 11.5, and that Fz3 is required for pathfinding by dopaminergic and serotonergic axons in the brain and by a subset of optic tract axons. In addition, conditional deletion of Fz3 in all tissues caudal to the neck eliminates the spinothalamic tract and the transmission of somatosensory information from the spinal cord to the brain, as determined by neuroanatomic tracing and behavioral testing.planar cell polarity | Cre/loxP C omplexity within the mammalian nervous system can be roughly divided into two categories: cell type identity and morphology/connectivity. On its largest scale, the second category is exemplified by the many distinct patterns of long-range axonal trajectories within the adult CNS. The guidance mechanisms responsible for these axonal trajectories have been an object of longstanding interest to neurobiologists, and, over the past 20 y, a wide variety of attractive and repulsive axon guidance systems have been identified (1). For a few well-defined axon growth and guidance decisions-such as dorsal vs. ventral growth of limb motor axons and midline crossing of retinal ganglion cell (RGC) and spinal sensory axons-the roles of several guidance systems, including Slit/Robo, Ephrin/Eph, and Semaphorin/Plexin, have been intensively investigated (2, 3).One recently discovered axon growth and guidance system uses some of the same molecular components that were identified in the context of epithelial polarity determination, a process referred to as tissue polarity or planar cell polarity (PCP). As first defined in Drosophila, PCP controls polarity within the plane of the epithelium and is mediated by a small number of integral membrane or membrane-associated proteins (4). Within the responsive epithelium, several PCP proteins are localized asymmetrically within each cell in a pattern that matches the large-scale vectorial asymmetry of the epithelium. In mice, two integral membrane PCP proteins, Frizzled3 (Fz3) and Celsr3, control a nearly identical set of axon growth and guidance processes, with loss-of-function mutations in either gene pro...

“…We found that in blind individuals, a subset of early visual cortices is active while solving math equations, and this activity scales with mathematical difficulty. Much evidence has documented responses to auditory and tactile stimuli in visual cortices of congenitally blind individuals (22)(23)(24)(25)(26)(27). The mechanisms and the scope of functional reorganization in cross-modal plasticity remain debated (43).…”

Section: Increased Functional Connectivity Between Visual Cortices Anmentioning

confidence: 99%

“…In blindness, "visual" areas of the brain are colonized by nonvisual functions. These occipital areas respond to auditory and tactile stimuli, a phenomenon termed cross-modal plasticity (22)(23)(24)(25). Some of these plastic responses appear to be related to higher-cognitive functions-most prominently, language processing and verbal memory (23,(25)(26)(27).…”

mentioning

confidence: 99%

Absence of visual experience modifies the neural basis of numerical thinking

Kanjlia

Lane

Feigenson

et al. 2016

133

In humans, the ability to reason about mathematical quantities depends on a frontoparietal network that includes the intraparietal sulcus (IPS). How do nature and nurture give rise to the neurobiology of numerical cognition? We asked how visual experience shapes the neural basis of numerical thinking by studying numerical cognition in congenitally blind individuals. Blind (n = 17) and blindfolded sighted (n = 19) participants solved math equations that varied in difficulty (e.g., 27 − 12 = x vs. 7 − 2 = x), and performed a control sentence comprehension task while undergoing fMRI. Whole-cortex analyses revealed that in both blind and sighted participants, the IPS and dorsolateral prefrontal cortices were more active during the math task than the language task, and activity in the IPS increased parametrically with equation difficulty. Thus, the classic frontoparietal number network is preserved in the total absence of visual experience. However, surprisingly, blind but not sighted individuals additionally recruited a subset of early visual areas during symbolic math calculation. The functional profile of these "visual" regions was identical to that of the IPS in blind but not sighted individuals. Furthermore, in blindness, number-responsive visual cortices exhibited increased functional connectivity with prefrontal and IPS regions that process numbers. We conclude that the frontoparietal number network develops independently of visual experience. In blindness, this number network colonizes parts of deafferented visual cortex. These results suggest that human cortex is highly functionally flexible early in life, and point to frontoparietal input as a mechanism of cross-modal plasticity in blindness.plasticity | blindness | number | development | vision N umerical reasoning pervades modern human culture. We readily represent quantity, whether thinking about apples, hours, people, or ideas. It has been suggested that this competence is rooted in a primitive nonsymbolic system of numerical representation that is shared among adults of diverse cultures, as well as with preverbal infants and nonhuman animals (1, 2). This nonsymbolic system allows these populations to estimate numbers of visual or auditory items and to compute over these quantities. For example, infants and monkeys can detect which of two arrays contains more items, and can add and subtract approximate quantities (1-4). The nonverbal, nonsymbolic system underlying this performance represents number in an inherently approximate way (5). However, numerate humans also have the unique ability to reason about quantities precisely using an acquired system of number symbols (5).Reasoning about approximate and exact number depends on a frontoparietal network, a key node of which is the intraparietal sulcus (IPS) (6). The IPS is active when participants estimate the number of items in a nonsymbolic display as well as when they solve symbolic math problems (e.g., 23 − 19 = x), with more IPS activity during hard math problems than easier ones (6, 7). Temporary dea...