Optokinetic nystagmus reflects perceptual directions in the onset binocular rivalry in Parkinson's disease.

Optokinetic nystagmus (OKN), the reflexive eye movements evoked by a moving field, has recently gained interest among researchers as a useful tool to assess conscious perception. When conscious perception and stimulus are dissociated, such as in binocular rivalry-when dissimilar images are simultaneously presented to each eye and perception alternates between the two images over time-OKN correlates with perception rather than with the physical direction of the moving field. While this relationship is well established in healthy subjects, it is yet unclear whether it also generalizes to clinical populations, for example, patients with Parkinson's disease. Parkinson's disease is a motor disorder, causing tremor, slow movements and rigidity. It may also be associated with oculomotor deficits, such as impaired saccades and smooth pursuit eye movements. Here, we employed short-duration, onset binocular rivalry (2 s trial of stimulus presentation followed by 1 s inter-trial interval) with moving grating stimuli to assess OKN in Parkinson's disease patients (N = 39) and controls (N = 29) of a similar age. Each trial was either non-rivalrous (same stimuli presented to both eyes) or rivalrous, as in binocular rivalry. We analyzed OKN to discriminate direction of stimulus and perception on a trial-by-trial basis. Although the speed of slow-phase OKN was slower in the patients, discriminability of conscious perception based on OKN was comparable between the groups. Treatment with anti-Parkinson drugs and deep brain stimulation improved motor ability of patients, but did not impact on OKN. Furthermore, OKN-based measures were robust and their latencies were shorter than manual button-based measures in both groups and stimulus conditions. To our knowledge, our study is the first to demonstrate that OKN can be used as a reliable indicator of conscious perception in binocular rivalry even in Parkinson's disease patients in whom impaired manual dexterity may render button-press reports less reliable.

The influence of light on temperature preference in Drosophila.

Ambient light affects multiple physiological functions and behaviors, such as circadian rhythms, sleep-wake activities, and development, from flies to mammals. Mammals exhibit a higher body temperature when exposed to acute light compared to when they are exposed to the dark, but the underlying mechanisms are largely unknown. The body temperature of small ectotherms, such as Drosophila, relies on the temperature of their surrounding environment, and these animals exhibit a robust temperature preference behavior. Here, we demonstrate that Drosophila prefer a ∼1° higher temperature when exposed to acute light rather than the dark. This acute light response, light-dependent temperature preference (LDTP), was observed regardless of the time of day, suggesting that LDTP is regulated separately from the circadian clock. However, screening of eye and circadian clock mutants suggests that the circadian clock neurons posterior dorsal neurons 1 (DN1(p)s) and Pigment-Dispersing Factor Receptor (PDFR) play a role in LDTP. To further investigate the role of DN1(p)s in LDTP, PDFR in DN1(p)s was knocked down, resulting in an abnormal LDTP. The phenotype of the pdfr mutant was rescued sufficiently by expressing PDFR in DN1(p)s, indicating that PDFR in DN1(p)s is responsible for LDTP. These results suggest that light positively influences temperature preference via the circadian clock neurons, DN1(p)s, which may result from the integration of light and temperature information. Given that both Drosophila and mammals respond to acute light by increasing their body temperature, the effect of acute light on temperature regulation may be conserved evolutionarily between flies and humans.

Temporal evolution of neural activity underlying auditory discrimination of frequency increase and decrease.

Discriminating a direction of frequency change is an important ability of the human auditory system, although temporal dynamics of neural activity underlying this discrimination remains unclear. In the present study, we recorded auditory-evoked potentials when human subjects explicitly judged a direction of a relative frequency change between two successive tones. A comparison of two types of trials with ascending and descending tone pairs revealed that neural activity discriminating a direction of frequency changes appeared as early as the P1 component of auditory-evoked potentials (latency 50 ms). Those differences between the ascending and descending trials were also observed in subsequent electroencephalographic components such as the N1 (100 ms) and P2 (200 ms). Furthermore, amplitudes of the P2 were significantly modulated by behavioral responses (upward/downward judgments) of subjects in the direction discrimination task, while those of the P1 were not. Those results indicate that, while the neural responses encoding a direction of frequency changes can be observed in an early component of electroencephalographic responses (50 ms after the change), the activity associated (correlated) with behavioral judgments evolves over time, being shaped in a later time period (around 200 ms) of the auditory processing.