Early blindness results in abnormal corticocortical and thalamocortical connections.

Studies in congenitally blind and bilaterally enucleated individuals show that an early loss of sensory driven activity can lead to massive functional reorganization. However, the anatomical substrate for this functional reorganization is unknown. In the present study, we examined patterns of corticocortical and thalamocortical connections in adult opossums that had been bilaterally enucleated neonatally, prior to the formation of retinogeniculate and geniculocortical connections. We show that in addition to normal thalamocortical projection patterns from visual nuclei, enucleated animals also receive input from nuclei associated with the somatosensory (ventral posterior nucleus, VP), auditory (medial geniculate nucleus, MGN), motor (ventrolateral nucleus, VL), and limbic/hippocampal systems (anterior dorsal nucleus, AD; and anterior ventral nucleus, AV). Likewise, in addition to normal corticocortical projections to area 17, bilaterally enucleated opossums also receive input from auditory, somatosensory, and multimodal cortex. These aberrant patterns of thalamocortical and corticocortical connections can account for alterations in functional organization observed in the visual cortex of bilateral enucleated animals, and indicate that factors extrinsic to the cortex play a large role in cortical field development and evolution. On the other hand, the maintenance of normal patterns of connections in the absence of visual input suggests that there are formidable constraints imposed on the developing cortex that highly restrict the types of evolutionary change possible.

Organization and connections of V1 in Monodelphis domestica.

We examined the internal organization and connections of the primary visual area, V1, in the South American marsupial Monodelphis domestica. Multiunit electrophysiological recording techniques were used to record from neurons at multiple sites. Receptive field location, size, progressions, and reversals were systematically examined to determine the visuotopic organization of V1 and its boundaries with adjacent visual areas. As in other mammals, a virtually complete representation of the visual hemifield was observed in V1, which was coextensive with a region of dense myelination. The vertical meridian was represented at the rostrolateral boundary of the field, the upper visual quadrant was represented caudolaterally, whereas the lower visual quadrant was represented rostromedially. Injections of fluorescent tracers into V1 revealed dense connections with cortex immediately adjacent to the rostrolateral boundary, in peristriate cortex (PS or V2). Connections were also consistently observed with a caudotemporal area (CT), entorhinal cortex (EC), and multimodal cortex (auditory/visual, A/V). These results demonstrate that M. domestica possess a highly differentiated neocortex with clear functional and architectonic cortical field boundaries, as well as discrete patterns of cortical connections. Some connections of V1 are similar to those observed in eutherian mammals, such as connections with V2 and extrastriate areas (e.g., CT), which suggests that there are general features of visual system organization that all mammals possess due to retention from a common ancestor. On the other hand, connections of V1 with EC and multimodal cortex may be a primitive feature of visual cortex that was lost in some lineages, may be a derived feature of marsupial neocortex, or may be a feature particular to mammals with small brains.

Formation of cortical fields on a reduced cortical sheet.

Theories of both cortical field development and cortical evolution propose that thalamocortical projections play a critical role in the differentiation of cortical fields (; ). In the present study, we examined how changing the size of the immature neocortex before the establishment of thalamocortical connections affects the subsequent development and organization of the adult neocortex. This alteration in cortex is consistent with one of the most profound changes made to the mammalian neocortex throughout evolution: cortical size. Removing the caudal one-third to three-fourths of the cortical neuroepithelial sheet unilaterally at an early stage of development in marsupials resulted in normal spatial relationships between visual, somatosensory, and auditory cortical fields on the remaining cortical sheet. Injections of neuroanatomical tracers into the reduced cortex revealed in an altered distribution of thalamocortical axons; this alteration allowed the maintenance of their original anteroposterior distribution. These results demonstrate the capacity of the cortical neuroepithelium to accommodate different cortical fields at early stages of development, although the anteroposterior and mediolateral relationships between cortical fields appear to be invariant. The shifting of afferents and efferents with cortical reduction or expansion at very early stages of development may have occurred naturally in different lineages over time and may be sufficient to explain much of the phenotypic variation in cortical field number and organization in different mammals.

Identification and modification of environmental noise in an ICU setting.

STUDY OBJECTIVES: Noise levels in the hospital setting are exceedingly high, especially in the ICU environment. We set out to determine what caused the noises producing sound peaks > or = 80 A-weighted decibels (dBA) in our ICU settings, and attempted to reduce the number of sound peaks > or = 80 dBA through a behavior modification program. DESIGN: The study was divided into two separate phases: noise identification and a trial of behavior modification. During the noise identification phase we simultaneously recorded sound peaks and the loudest noise heard subjectively by one observer in the medical ICU (MICU) and the respiratory ICU (RICU). During the behavior modification phase of the study we implemented a behavior modification program, geared toward noise reduction, in all of the MICU staff. Sound levels were monitored before and at the end of the behavior modification trial. SETTING: The MICU and RICU of a 720-bed teaching hospital in Providence, RI. PARTICIPANTS: All ICU staff during the study period. INTERVENTIONS: Once the noises that were determined to be amenable to behavior modification were identified, a behavior modification program was conducted during a 3-week period in our MICU. Baseline and post-behavior modification noise recordings were compared in 6-h intervals after sites were matched by number of patients in a room and Acute Physiology and Chronic Health Evaluation II (APACHE II) scores. MEASUREMENTS AND RESULTS: We identified several causes of sound peaks > or = 80 dBA amenable to behavior modification; television and talking accounted for 49%. We also significantly reduced the 24-h mean peak noise level (p=0.0001), as well as the mean peak noise level (p=0.0001) and the number of sound peaks > or = 80 dBA (p=0.0001) in all 6-h blocks except for the 12 AM to 6 AM period. CONCLUSIONS: We conclude that many of the noises causing sound peaks > or =80 dBA are amenable to behavior modification and that it is possible to reduce the noise levels in an ICU setting significantly through a program of behavior modification.

Lowering the legal blood alcohol level for motorcyclists.

The blood alcohol concentrations (BAC) of all operators involved in motorcycle accidents (MCA) and drivers of motor vehicle accidents (MVA) admitted to a New Jersey Level I Trauma Center during 1992 (the first year such data were computerized) were evaluated. Comparable to other institutional statistics (one-third of vehicular accidents are related to alcohol consumption) our data showed 13 (33%) of 40 MCA operators and 117 (35%) of 340 MVA drivers had measurable BAC. These values, as well as their respective Injury Severity Scores (ISS), were recorded and compared for significance of apparent differences using the 't' test for unpaired observations. Mean BAC was 124 +/- 24 (SE) mg dl-1 for MCA and 180 +/- 9 mg dl-1 for MVA (p < 0.05). The respective mean ISS for MCA was 13.1 +/- 5.4 and MVA was 7.9 +/- 0.9 (p = 0.12). These data indicate that drivers involved in MVA and MCA are frequently under the influence of alcohol. The mean BAC for motorcyclists is significantly less than that for drivers of four-wheeled passenger vehicles and is likely to reflect the need for greater coordination and balance when operating a two-wheeled vehicle.

The efficacy of oral appliances in the treatment of persistent sleep apnea after uvulopalatopharyngoplasty.

Twenty-four patients who failed uvulopalatopharyngoplasty (UPPP) for obstructive sleep apnea (OSA) had an adjustable oral (Herbst) appliance made to treat the persistent apnea. Six patients discontinued the device prior to sleep evaluation. Eighteen patients had polysomnographic evaluations at baseline, post-UPPP, and with the Herbst appliance in place. The apnea-hypopnea index baseline (AHI) and arterial oxygen saturation (SaO2) nadir were 42.3+/-6.1 and 83.6+/-1.8%, respectively. There was no significant change in either parameter with surgery. With the oral appliance, the AHI fell to 15.3+/-4.4 (p < or = 0.01) and the SaO2 nadir increased to 87.9+/-1.2% (p < or = 0.05). Ten of the patients had control of the OSA with the Herbst appliance with a fall in the AHI to < 10. There were, in addition, two partial responders as defined by an AHI of <20 and a >50% fall in AHI compared with baseline and post-UPPP values. All but one of the responders and partial responders had complete resolution of subjective symptoms of daytime sleepiness with the appliance. An adjustable oral appliance appears to be an effective mode of therapy to control OSA after an unsuccessful UPPP.