Correction: Iliescu, B.F. Learning by Exposure in the Visual System. Brain Sci. 2022, 12, 508.

Bryan Hansen and Valentin Dragoi were previously included as authors in the publication [...].

Learning by Exposure in the Visual System.

It is increasingly being understood that perceptual learning involves different types of plasticity. Thus, whereas the practice-based improvement in the ability to perform specific tasks is believed to rely on top-down plasticity, the capacity of sensory systems to passively adapt to the stimuli they are exposed to is believed to rely on bottom-up plasticity. However, top-down and bottom-up plasticity have never been investigated concurrently, and hence their relationship is not well understood. To examine whether passive exposure influences perceptual performance, we asked subjects to test their orientation discrimination performance around and orthogonal to the exposed orientation axes, at an exposed and an unexposed location while oriented sine-wave gratings were presented in a fixed position. Here we report that repetitive passive exposure to oriented sequences that are not linked to a specific task induces a persistent, bottom-up form of learning that is stronger than top-down practice learning and generalizes across complex stimulus dimensions. Importantly, orientation-specific exposure learning led to a robust improvement in the discrimination of complex stimuli (shapes and natural scenes). Our results indicate that long-term sensory adaptation by passive exposure should be viewed as a form of perceptual learning that is complementary to practice learning in that it reduces constraints on speed and generalization.

One-step endovascular treatment of bilateral traumatic carotid-cavernous fistulae with atypical clinical course.

Traumatic carotid-cavernous fistula (TCCF) is a rare neurovascular pathologic entity. The bilateral form occurs even rarer and given the potential risk for both optic tracts presents an urgent indication for quick and effective treatment. We present a patient with a bilateral Barrow type A TCCF with a fulminant development of symptoms, who was successfully treated with bilateral detachable balloons in a single session endovascular procedure. The patient experienced complete relief of symptoms, however the complete neurological deficit in the left optic nerve was persistent.

Adaptive changes in neuronal synchronization in macaque V4.

A fundamental property of cortical neurons is the capacity to exhibit adaptive changes or plasticity. Whether adaptive changes in cortical responses are accompanied by changes in synchrony between individual neurons and local population activity in sensory cortex is unclear. This issue is important as synchronized neural activity is hypothesized to play an important role in propagating information in neuronal circuits. Here, we show that rapid adaptation (300 ms) to a stimulus of fixed orientation modulates the strength of oscillatory neuronal synchronization in macaque visual cortex (area V4) and influences the ability of neurons to distinguish small changes in stimulus orientation. Specifically, rapid adaptation increases the synchronization of individual neuronal responses with local population activity in the gamma frequency band (30-80 Hz). In contrast to previous reports that gamma synchronization is associated with an increase in firing rates in V4, we found that the postadaptation increase in gamma synchronization is associated with a decrease in neuronal responses. The increase in gamma-band synchronization after adaptation is functionally significant as it is correlated with an improvement in neuronal orientation discrimination performance. Thus, adaptive synchronization between the spiking activity of individual neurons and their local population can enhance temporally insensitive, rate-based-coding schemes for sensory discrimination.

Attention alters visual plasticity during exposure-based learning.

It is generally believed that attention enhances the processing of sensory information during perception and learning. Here we report that, contrary to common belief, attention limits the degree of plasticity induced by repeated exposure to image features. Specifically, daily exposure to oriented stimuli that are not linked to a specific task causes an orientation-specific improvement in perceptual performance along the "exposed" axes. This effect is modulated by attention: human subjects showed a larger improvement in orientation discrimination when attention is directed toward the location where stimuli are presented. However, the capacity to perform discriminations away from the exposed orientation is enhanced when the exposure stimuli are unattended. Importantly, the improvement in orientation discrimination at the unattended location leads to a robust enhancement in the discrimination of complex stimuli, such as natural texture images, with orientation components along the exposed axes, whereas the improvement in orientation discrimination at the attended location exhibits only weak transfer to complex stimuli. These results indicate that sensory adaptation by passive stimulus exposure should be viewed as a form of perceptual learning that is complementary to practice-based learning in that it reduces constraints on generalization.