Forensic application of inverse and reverse projection photogrammetry to determine subject location and orientation when both camera and subject move relative to the scene.

We present a case study of a mountain bicycle accident captured by the rider's chest-mounted action camera. The objective of the investigation was to determine the orientation of the bicycle relative to the ground and the location of the rider's center of gravity relative to the bicycle. The problem faced in the investigation was that the camera was moving relative to the scene and rider, and the bicycle was moving relative to the camera. Inverse photogrammetry was used to determine the location and orientation of the camera relative to the scene. Reverse projection photogrammetry applied to an exemplar bicycle provided an estimate of the location and orientation of the bicycle relative to the camera. The rider's position and orientation relative to the camera were estimated by comparing synchronized side views and chest-mounted action camera views of the rider's movements, recorded during a trail descent prior to the accident.

Representation of the body in the lateral striatum of the freely moving rat: Fast Spiking Interneurons respond to stimulation of individual body parts.

Numerous studies have shown that certain types of striatal interneurons play a crucial role in selection and regulation of striatal output. Striatal Fast-Spiking Interneurons (FSIs) are parvalbumin positive, GABAergic interneurons that constitute less than 1% of the total striatal population. It is becoming increasingly evident that these sparsely distributed neurons exert a strong inhibitory effect on Medium Spiny projection Neurons (MSNs). MSNs in lateral striatum receive direct synaptic input from regions of cortex representing discrete body parts, and show phasic increases in activity during touch or movement of specific body parts. In the present study, we sought to determine whether lateral striatal FSIs identified by their electrophysiological properties, i.e., short-duration spike and fast firing rate (FR), display body part sensitivity similar to that exhibited by MSNs. During video recorded somatosensorimotor exams, each individual body part was stimulated and responses of single neurons were observed and quantified. Individual FSIs displayed patterns of activity related selectively to stimulation of a discrete body part. Most patterns of activity were similar to those exhibited by typical MSNs, but some phasic decreases were observed. These results serve as evidence that some striatal FSIs process information related to discrete body parts and participate in sensorimotor processing by striatal networks that contribute to motor output. STATEMENT OF SIGNIFICANCE: Parvalbumin positive, striatal FSIs are hypothesized to play an important role in behavior by inhibiting MSNs. We asked a fundamental question regarding information processed during behavior by FSIs: whether FSIs, which preferentially occupy the sensorimotor portion of the striatum, process activity of discrete body parts. Our finding that they do, in a selective manner similar to MSNs, begins to reveal the types of phasic signals that FSI feed forward to projection neurons during striatal processing of cortical input regarding a specific sensorimotor event. These findings suggest new avenues for testing feed-forward inhibition theory as applied to striatum in naturalistic conditions, such as whether FSI decreases facilitate excitation of MSNs related to the current movement while FSI increases silence MSNs unrelated to the current movement.