Interhemispheric visual competition after multisensory reversal of hemianopia

Unilateral lesions of visual cortex have the secondary consequence of suppressing visual circuits in the midbrain superior colliculus (SC), collectively producing blindness in contralesional space (“hemianopia”). Recent studies have demonstrated that SC visual responses and contralesional vision can be reinstated by a non‐invasive multisensory training procedure in which spatiotemporally concordant visual‐auditory pairs are repeatedly presented within the blind hemifield. Despite this recovery of visual responsiveness, the loss of visual cortex was expected to result in permanent deficits in that hemifield, especially when visual events in both hemifields compete for attention and access to the brain's visuomotor circuitry. This was evaluated in the present study in a visual choice paradigm in which the two visual hemifields of recovered cats were simultaneously stimulated with equally valent visual targets. Surprisingly, the expected disparity was not found, and some animals even preferred stimuli presented in the previously blind hemifield. This preference persisted across multiple stimulus intensity levels and there was no indication that animals were less aware of cues in the previously blind hemifield than in its spared counterpart. Furthermore, when auditory cues were combined with visual cues, the enhanced performance they produced on a visual task was no greater in the normal than in the previously blind hemifield. These observations suggest that the multisensory rehabilitation paradigm revealed greater inherent visual information processing potential in the previously blind hemifield than was believed possible given the loss of visual cortex.     

血管痉挛对蛛网膜下腔出血后脑血管病理性改变的影响

目的探讨蛛网膜下腔出血(SAH)性脑血管痉挛(CVS)与血管壁病理学改变之间的因果关系。方法采用药理学预阻滞法,通过光镜和电镜对42只猫SAH后CVS的形成及其对血管壁病理性改变的影响作用进行观察。结果预先使用血管外周阻滞剂可以明显地减轻SAH所致的CVS反应程度,并使血管壁发生的病理性改变也随之减轻。结论 CVS是血管壁发生病理性改变的成因,继而又成为影响SAH预后的主要原因之一。预防或阻止CVS的发生,可有效地防止血管壁发生相应的病理学改变。     

Differences in spatial and temporal frequency interactions between central and peripheral parts of the feline area 18

The visual system demonstrates significant differences in information processing abilities between the central and peripheral parts of the visual field. Optical imaging based on intrinsic signals was used to investigate the difference in stimulus spatial and temporal frequency interactions related to receptive field eccentricity in the cat area 18. Changing either the spatial or the temporal frequency of grating stimuli had a significant impact on responses in the cortical areas corresponding to the centre of the visual field and more peripheral parts at 10 degrees eccentricity. The cortical region corresponding to the centre of the gaze was tuned to 0.4 cycles per degree (c/deg) for spatial frequency and 2 Hz for temporal frequency. In contrast, the cortical region corresponding to the periphery of the visual field was tuned to a lower spatial frequency of 0.15 c/deg and a higher temporal frequency of 4 Hz. Interestingly, when we simultaneously changed both the spatial frequency and the temporal frequency of the grating stimuli, the responses were significantly different from those estimated with an assumption of independence between the spatial and temporal frequency in the cortical region corresponding to the periphery of the visual field. However, in the cortical area corresponding to the centre of the gaze, spatial frequency showed significant independence from temporal frequency. These properties support the notion of relative specialization of visual information processing for peripheral representations in cortical areas.     

Feline mitochondrial DNA sampling for forensic analysis: When enough is enough!

Pet hair has a demonstrated value in resolving legal issues. Cat hair is chronically shed and it is difficult to leave a home with cats without some level of secondary transfer. The power of cat hair as an evidentiary resource may be underused because representative genetic databases are not available for exclusionary purposes. Mitochondrial control region databases are highly valuable for hair analyses and have been developed for the cat. In a representative worldwide data set, 83% of domestic cat mitotypes belong to one of twelve major types. Of the remaining 17%, 7.5% are unique within the published 1394 sample database. The current research evaluates the sample size necessary to establish a representative population for forensic comparison of the mitochondrial control region for the domestic cat. For most worldwide populations, randomly sampling 50 unrelated local individuals will achieve saturation at 95%. The 99% saturation is achieved by randomly sampling 60–170 cats, depending on the numbers of mitotypes available in the population at large. Likely due to the recent domestication of the cat and minimal localized population substructure, fewer cats are needed to meet mitochondria DNA control region database practical saturation than for humans or dogs. Coupled with the available worldwide feline control region database of nearly 1400 cats, minimal local sampling will be required to establish an appropriate comparative representative database and achieve significant exclusionary power.     

Effects of Reflex Middle-Ear Muscle Contractions on Cochlear Responses to Bone-Conducted Sound

The effects of contralaterally elicited middle-ear muscle (MEM) reflexes on cochlear microphonic responses to air- and bone-conducted tones were examined in decerebrate cats. Stapedius effects on bone conduction were almost identical in configuration and amplitude to those on air conduction at all frequencies. However, tensor tympani effects were more complex, the configuration of the bone-conduction effects varying with the location of the transducer on the skull and with frequency. The relative contributions of the two muscles to the effects of joint contractions varied markedly between animals. It is suggested that non-reflex MEM contractions associated with activity of the facial musculature might provide protection against masking of environmental sounds by the low-frequency bone-conducted sound generated by such activity     

Evaluation of a Thin-film Peripheral Nerve Cuff Electrode

Abstract

This is a study of the reaction of large nerves to implantation using a flexible, thin-film cuff electrode. Cuff electrodes were implanted on the sciatic nerve of three cats. An implantation period of six weeks allowed sufficient time for any injury responses in the nerve and connective tissue sheath around the cuff to develop. The electrode came off the nerve in one of the cats. In the remaining two cats, gross observation following explantation of the electrodes revealed encapsulation of the cuffs without swelling of nerve tissue. Histological evaluation did not demonstrate nerve injury. The nerve cuff electrodes, which are comprised of titanium and iridium coatings on a fluorocarbon polymer substrate, appeared unaffected by the implantation, and connective tissue encapsulation did not adhere to either the polymer substrate or metallization. Evaluation of the electrodes using activated iridium oxide charge injection sites in more extended studies is now being undertaken. (J Spinal Cord Med; 18:28–32)     

Posttraumatic Early Epilepsy and Minor Head Injury

The mechanism of “early epilepsy” sometimes observed after trivial head injury is controversial. Also, the risk of developing late epilepsy after these convulsions, so far, have not been clear.

In order to clarify the mechanism of this posttraumatic early epilepsy after trivial head injury, an attempt was made to observe the role of extracellular potassium ion concentration ([K⁺]_o) in initiation of seizure discharges, in both adult cats and kittens, with K-sensitive microelectrodes.

It was concluded that an increase of [K⁺]_o was not a simple factor for epileptogenesis but minor head injury actually increased seizure slisceptability of immature cat cortex.