Connectome alterations following perinatal deafness in the cat.

Following sensory deprivation, areas and networks in the brain may adapt and reorganize to compensate for the loss of input. These adaptations are manifestations of compensatory crossmodal plasticity, which has been documented in both human and animal models of deafness-including the domestic cat. Although there are abundant examples of structural plasticity in deaf felines from retrograde tracer-based studies, there is a lack of diffusion-based knowledge involving this model compared to the current breadth of human research. The purpose of this study was to explore white matter structural adaptations in the perinatally-deafened cat via tractography, increasing the methodological overlap between species. Plasticity was examined by identifying unique group connections and assessing altered connectional strength throughout the entirety of the brain. Results revealed a largely preserved connectome containing a limited number of group-specific or altered connections focused within and between sensory networks, which is generally corroborated by deaf feline anatomical tracer literature. Furthermore, five hubs of cortical plasticity and altered communication following perinatal deafness were observed. The limited differences found in the present study suggest that deafness-induced crossmodal plasticity is largely built upon intrinsic structural connections, with limited remodeling of underlying white matter.

The gradient in gray matter thickness across auditory cortex and differential cortical thickness changes following perinatal deafness.

In the absence of hearing during development, the brain adapts and repurposes what was destined to become auditory cortex. As cortical thickness is commonly used as a proxy to identify cortical regions that have undergone plastic changes, the purpose of this investigation was to compare cortical thickness patterns between hearing and deaf cats. In this study, normal hearing (n = 29) and deaf (n = 26) cats were scanned to examine cortical thickness in hearing controls, as well as differential changes in thickness as a consequence of deafness. In hearing cats, a gradient in cortical thickness was identified across auditory cortex in which it is thinner in more dorsal regions and thicker in more ventral regions. Compared with hearing controls, differential thickening and thinning was observed in specific regions of deaf auditory cortex. More dorsal regions were found to be bilaterally thicker in the deaf group, while more ventral regions in the left hemisphere were thinner. The location and nature of these changes creates a gradient along the dorsoventral axis, wherein dorsal auditory cortical fields are thicker, whereas more ventral fields are thinner in deaf animals compared with hearing controls.

The limited capacity of visual temporal integration in cats.

It has been long known that prolonging stimulus duration may increase the perceived brightness of a visual stimulus. The interaction between intensity and duration generally follows a rule, such as that described in Bloch's law. This visual temporal integration relationship has been identified in human subjects and in non-human primates. However, although auditory temporal integration has been extensively studied in the cat, visual temporal integration has not. Therefore, the goal of this study was to examine visual temporal integration in the cat. We trained five cats to respond when a brief luminance change was detected in a fixation dot. After training, we measured the success rate of detecting the luminance change with varying durations at threshold, subthreshold, and suprathreshold luminance levels. Psychometric functions showed that prolonging stimulus duration improved task performance, more noticeably for stimuli below 100 ms than beyond. Most psychometric functions were better fit to an exponential model than to a linear model. The gradually saturated performance observed here, as in previous studies, can be explained by the "leaky integrator" hypothesis, that is, temporal integration is only valid below a critical duration. Overall, we developed a task whereby visual temporal integration was successfully demonstrated in the cat. The effect of stimulus duration on detection success rate displayed a pattern generally consistent with previous human and non-human primate findings on visual temporal integration.