Pérez ML, Shanbhag SJ, Peña JL. Auditory spatial tuning at the crossroads of the midbrain and forebrain. J Neurophysiol 102: 1472-1482, 2009. First published July 1, 2009 doi:10.1152/jn.00400.2009. The barn owl's midbrain and forebrain contain neurons tuned to sound direction. The spatial receptive fields of these neurons result from sensitivity to combinations of interaural time (ITD) and level (ILD) differences over a broad frequency range. While a map of auditory space has been described in the midbrain, no similar topographic representation has been found in the forebrain. The first nuclei that belong exclusively to the forebrain and midbrain pathways are the thalamic nucleus ovoidalis (Ov) and the external nucleus of the inferior colliculus (ICx), respectively. The midbrain projects to the auditory thalamus before sharp spatial receptive fields emerge; although Ov and ICx receive projections from the same midbrain nuclei, they are not directly connected. We compared the spatial tuning in Ov and ICx. Thalamic neurons respond to a broader frequency range and their ITD and ILD tuning varied more across frequency. However, neurons in Ov showed spatial receptive fields as selective as neurons in ICx. Thalamic spatial receptive fields were tuned to frontal and contralateral space and correlated with their tuning to ITD and ILD. Our results indicate that spatial tuning emerges in both pathways by similar combination selectivity to ITD and ILD. However, the midbrain and the thalamus do not appear to repeat exactly the same processing, as indicated by the difference in frequency range and the broader tuning to binaural cues. The differences observed at the initial stages of these soundlocalization pathways may reflect diverse functions and coding schemes of midbrain and forebrain.

Pérez, María Lucía and José Luis Peña. Comparison of midbrain and thalamic space-specific neurons in barn owls. J Neurophysiol 95: 783-790, 2006; doi:10.1152/jn.00833.2005. Spatial receptive fields of neurons in the auditory pathway of the barn owl result from the sensitivity to combinations of interaural time (ITD) and level differences across stimulus frequency. Both the forebrain and tectum of the owl contain such neurons. The neural pathways, which lead to the forebrain and tectal representations of auditory space, separate before the midbrain map of auditory space is synthesized. The first nuclei that belong exclusively to either the forebrain or the tectal pathways are the nucleus ovoidalis (Ov) and the external nucleus of the inferior colliculus (ICx), respectively. Both receive projections from the lateral shell subdivision of the inferior colliculus but are not interconnected. Previous studies indicate that the owl's tectal representation of auditory space is different from those found in the owl's forebrain and the mammalian brain. We addressed the question of whether the computation of spatial cues in both pathways is the same by comparing the ITD tuning of Ov and ICx neurons. Unlike in ICx, the relationship between frequency and ITD tuning had not been studied in single Ov units. In contrast to the conspicuous frequency independent ITD tuning of space-specific neurons of ICx, ITD selectivity varied with frequency in Ov. We also observed that the spatially tuned neurons of Ov respond to lower frequencies and are more broadly tuned to ITD than in ICx. Thus there are differences in the integration of frequency and ITD in the two sound-localization pathways. Thalamic neurons integrate spatial information not only within a broader frequency band but also across ITD channels.

IntroductionIntravenous crystalloid fluid resuscitation forms a crucial part of the early intervention bundle for sepsis and septic shock, with the Surviving Sepsis Campaign guidelines recommending a 30 mL/kg fluid bolus within the first hour. Compliance with this suggested target varies in patients with comorbidities such as congestive heart failure, chronic kidney disease and cirrhosis due to concerns regarding iatrogenic fluid overload. However, it remains unclear whether resuscitation with higher fluid volumes puts them at greater risk of adverse outcomes. Thus, this systematic review will synthesise evidence from existing studies to assess the effects of a conservative as compared with a liberal approach to fluid resuscitation in patients at greater perceived risk of fluid overload due to comorbid conditions.Methods and analysisThis protocol was registered on PROSPERO and has been drafted following the checklist of Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols. We will search MEDLINE, MEDLINE Epub Ahead of Print and In-Process, In-Data-Review & Other Non-Indexed Citations, Embase, Embase Classic, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, Web of Science Core Collection, CINAHL Complete and ClinicalTrials.gov. A preliminary search of these databases was performed from their inception to 30 August 2022. The risk of bias and random errors will be assessed using the revised Cochrane risk-of-bias tool for randomised clinical trials and the Newcastle-Ottawa Scale for case–control and cohort studies. If a sufficient number of comparable studies are identified, we will perform a meta-analysis applying random effects model. We will investigate heterogeneity using a combination of visual inspection of the funnel plot as well as the Egger’s test.Ethics and disseminationNo ethics approval is required for this study since no original data will be collected. The findings will be disseminated through peer-reviewed publication and conference presentation.PROSPERO registration numberCRD42022348181.