Inhomogeneous Encoding of the Visual Field in the Mouse Retina.

Stimulus characteristics of the mouse's visual field differ above and below the skyline. Here, we show for the first time that retinal ganglion cells (RGCs), the output neurons of the retina, gradually change their functional properties along the ventral-dorsal axis to allow better representation of the different stimulus characteristics. We conducted two-photon targeted recordings of transient-Offα-RGCs and found that they gradually became more sustained along the ventral-dorsal axis, revealing >5-fold-longer duration responses in the dorsal retina. Using voltage-clamp recordings, pharmacology, and genetic manipulation, we demonstrated that the primary rod pathway underlies this variance. Our findings challenge the current belief that RGCs of the same subtype exhibit the same light responses, regardless of retinal location, and suggest that networks underlying RGC responses may change with retinal location to enable optimized sampling of the visual image.

Reduced mind wandering in patients with Parkinson's disease.

BACKGROUND: Mind Wandering (MW) refers to the process of disengaging from the immediate external environment and participating in internally driven mentation. This process has been suggested to be supported by a distributed set of brain regions, collectively referred to as the Default Mode Network (DMN). Recently, reduced recruitment and connectivity of the DMN has been described in Parkinson's disease (PD) patients compared to healthy controls. We thus aimed to explore whether PD patients with normal cognitive test scores show differential MW capabilities compared to healthy controls. METHODS: Thirty PD patients and thirty age-matched controls, all with a Montreal cognitive assessment (MoCA) score of 26 or above, performed a novel yet validated thought-sampling paradigm used to assess the frequency and extent of MW irrespective of cognitive load in which participants were asked to observe a series of geometric shapes and describe their thoughts after watching them. Shapes were presented one at a time for varying durations across nine trials. RESULTS: PD patients showed significantly less MW compared to the control. ANCOVA revealed a significant interaction indicating that the difference in MW scores was driven by trials with short stimulus presentation times. CONCLUSIONS: These findings provide evidence for decreased MW in PD patients. We propose that this is due to difficulties in performing MW within short time frames.

Invariant Temporal Dynamics Underlie Perceptual Stability in Human Visual Cortex.

An inherent limitation of human visual system research stems from its reliance on highly controlled laboratory conditions. Visual processing in the real world differs substantially from such controlled conditions. In particular, during natural vision, we continuously sample the dynamic environment by variable eye movements that lead to inherent instability of the optical image. The neuronal mechanism by which human perception remains stable under these natural conditions remains unknown. Here, we examined a neural mechanism that may contribute to such stability, i.e., the extent to which neuronal responses remain invariant to oculomotor parameters and viewing conditions. To this end, we introduce an experimental paradigm in which intracranial brain activity, a video of the real-life visual scene, and free oculomotor behavior were simultaneously recorded in human patients. Our results reveal, in high-order visual areas, a remarkable level of neural invariance to the length of eye fixations and lack of evidence for a saccade-related neuronal signature. Thus, neuronal responses, while showing high selectivity to the category of visual images, manifested stable "iconic" dynamics. This property of invariance to fixation onset and duration emerged only in high-order visual representations. In early visual cortex, the fixation onset was accompanied with suppressive neural signal, and duration of neuronal responses was largely determined by the fixation times. These results uncover unique neuronal dynamics in high-order ventral stream visual areas that could play an important role in achieving perceptual stability, despite the drastic changes introduced by oculomotor behavior in real life.