Asymmetrical organization of oral structures in the primary and secondary somatosensory cortices in rats: An optical imaging study

In rodents, the representation of the body surface in the primary somatosensory cortex (S1) forms a mirror image along the ventral border of the S1 in the secondary somatosensory cortex (S2). Sensory information from the oral region is processed in the S1 and the border region between the S2 and insular oral region (IOR). We examined the relationship between somatosensory representations in the S1 and S2/IOR using optical imaging with a voltage-sensitive dye in urethane-anesthetized rats. In reference to the rhinal fissure and middle cerebral artery, we made a somatosensory map by applying electrical or air puff stimulation. The initial neural excitation in the S1 to facial structures, including the eyebrow, cornea, pinna, whisker pad, nasal tip, and nasal mucosa, spread toward the ventral area, putatively the S2. The initial cortical responses in the S1 to oral structures, including the lower lip, tongue, and teeth, were spatially separated from those in the S2/IOR. The representation of the tongue center, tongue tip, mandibular molar pulp, mandibular incisor pulp, and mandibular incisor periodontal ligament were almost linearly arranged from caudal to rostral in both S1 and S2/IOR. The lower lip was represented in the dorsal area from the representation of teeth and tongue in both S1 and S2/IOR. The representations of maxillary teeth were caudal and dorsal to the representations of mandibular teeth in the S1 and S2/IOR, respectively. These results suggest that the representation of oral structures in the S1 formed a non-mirror image, not a mirror image, in the S2/IOR. This article is protected by copyright. All rights reserved.

Air Puff System Fundamentals for Reproducible Eyeblink Conditioning Research

Air puff systems are at once trivially straightforward and dauntingly complex. On the one hand, they are little but a pressure source, valve, and tube connected together. On the other, the air passing through them is a compressible medium, expanding approximately adiabatically while travelling at high velocity through a compliant tube, and exiting as a turbulent jet with velocity peak and profile varying non-linearly in its near-field. This complexity puts precise mathematical prediction of puff properties out of reach of most labs. There are, however, a number of phenomena fundamental to air puff system design that are worth understanding to a first order of approximation, or at least qualitatively. Using a simplified, “electronic–hydraulic analogy” model, this paper discusses these phenomena in just enough depth for the reader to confidently specify parts for an air puff delivery system, to measure its key parameters, and/or to describe a given system unambiguously in publications, thus maximizing reproducibility.

Dynamic optical coherence tomography measurements of elastic wave propagation in tissue-mimicking phantoms and mouse cornea in vivo

We demonstrate the use of phase-stabilized swept-source optical coherence tomography to assess the propagation of low-amplitude (micron-level) waves induced by a focused air-pulse system in tissue-mimicking phantoms, a contact lens, a silicone eye model, and the mouse cornea in vivo. The results show that the wave velocity can be quantified from the analysis of wave propagation, thereby enabling the estimation of the sample elasticity using the model of surface wave propagation for the tissue-mimicking phantoms. This noninvasive, noncontact measurement technique involves low-force methods of tissue excitation that can be potentially used to assess the biomechanical properties of ocular and other delicate tissues in vivo.

Contributing factors to corneal deformation in air puff measurements

PURPOSE

Air puff systems have been presented recently to measure corneal biomechanical properties in vivo. In our study we tested the influence of several factors on corneal deformation to an air puff: IOP, corneal rigidity, dehydration, presence of sclera, and in vivo versus in vitro conditions.

METHODS

We used 14 freshly enucleated porcine eyes and five human donor eyes for in vitro experiments; nine human eyes were used for in vivo experiments. Corneal deformation was studied as a function of: IOP ranging from 15 to 45 mm Hg (in vitro); dehydration after riboflavin-dextran instillation (in vitro); corneal rigidity after standard ultraviolet (UV) corneal crosslinking (CXL, in vitro); boundary conditions, that is effect of the presence of the sclera (comparing corneal buttons and whole globes in vitro in pigs); and effect of ocular muscles (comparing human whole globes in vitro and in vivo). The temporal corneal deformation was characterized by the apex indentation across time, the maximal indentation depth, and the temporal symmetry (comparing inward versus outward deformation). The spatial corneal profile was characterized by the peak distance at maximal deformation.

RESULTS

Temporal and spatial deformation profiles were very sensitive to the IOP (P < 0.001). The sclera slightly affected the temporal symmetry, while the ocular muscles drastically changed the amount of corneal recovery. CXL produced a significant (P = 0.001) reduction of the cornea indentation (by a factor of 1.41), and a change in the temporal symmetry of the corneal deformation profile (by a factor of 1.65), indicating a change in the viscoelastic properties with treatment.

CONCLUSIONS

Corneal deformation following an air puff allows the measurement of dynamic properties, which are essential for the characterization of corneal biomechanics.