Although the firing patterns of collision-detecting neurons have been described in detail in several species, the mechanisms generating responses in these neurons to visual objects on a collision course remain largely unknown. This is partly due to the limited number of intracellular recordings from such neurons, particularly in vertebrate species. By employing patch recordings in a novel integrated frog eye-tectum preparation we tested the hypothesis that OFF retinal ganglion cells were driving the responses to visual objects on a collision course in the frog optic tectum neurons. We found that the majority (22/26) of neurons in layer 6 responding to visual stimuli fitted the definition of η class collision-detectors: they readily responded to a looming stimulus imitating collision but not a receding stimulus (spike count difference ∼10 times) and the spike firing rate peaked after the stimulus visual angle reached a threshold value of ∼20-45°. In the majority of these neurons (15/22) a slow frequency oscillation (f=∼20Hz) of the neuronal membrane potential could be detected in the responses to a simulated collision stimulus, as well as to turning off the lights. Since OFF retinal ganglion cells could produce such oscillations, our observations are in agreement with the hypothesis that 'collision' responses in the frog optic tectum neurons are driven by synaptic inputs from OFF retinal ganglion cells.
Herpetological inventories conducted in the Pui Pui Protected Forest in the central Peruvian Andes between 2012 and 2014 revealed unusually high local anuran richness and endemism. Herein, we describe a new species of discovered in the buffer zone of the protected area between 1550 and 1730 m a.s.
- A new species of leaf litter toad has been identified in Dayaoshan National Nature Reserve, Guangxi, China, using genetic, physical, and sound analysis.
- Key distinguishing features include medium size, rough dorsal skin, black spots on flanks, and specific throat and ventral surface colors, among others.
- This toad breeds between March and April in evergreen forests at elevations of 1,000 to 1,600 meters.
Light pulses in the femtosecond range require sophisticated methods for their precise temporal characterization. Several techniques have been developed over the past decades that deliver the temporal structure of ultrashort light pulses. Still, there are special cases left that cannot be treated directly by established methods.
In situ characterization of the electric field of ultrafast pulses is critical in multiphoton microscopy. Although second harmonic generation-based collinear Frequency-Resolved Optical Gating (FROG) addresses this need, the interferometric measurement is challenged by interferometric drift instability, the required high sampling density of the acquired data, and the inability to directly use the interferometric data with conventional FROG retrieval algorithms. We address these issues by combining low-pass Fourier filtering with active kHz dithering of the interferometric path length difference using a piezo-driven retroreflector.
Natural visual scenes are dominated by spatiotemporal image dynamics, but how the visual system integrates "movie" information over time is unclear. We characterized optic tectal neuronal receptive fields using sparse noise stimuli and reverse correlation analysis. Neurons recognized movies of ~200-600 ms durations with defined start and stop stimuli.
