Tapered fibertrodes for optoelectrical neural interfacing in small brain volumes with reduced artefacts.

Deciphering the neural patterns underlying brain functions is essential to understanding how neurons are organized into networks. This deciphering has been greatly facilitated by optogenetics and its combination with optoelectronic devices to control neural activity with millisecond temporal resolution and cell type specificity. However, targeting small brain volumes causes photoelectric artefacts, in particular when light emission and recording sites are close to each other. We take advantage of the photonic properties of tapered fibres to develop integrated 'fibertrodes' able to optically activate small brain volumes with abated photoelectric noise. Electrodes are positioned very close to light emitting points by non-planar microfabrication, with angled light emission allowing the simultaneous optogenetic manipulation and electrical read-out of one to three neurons, with no photoelectric artefacts, in vivo. The unconventional implementation of two-photon polymerization on the curved taper edge enables the fabrication of recoding sites all around the implant, making fibertrodes a promising complement to planar microimplants.

Depth-resolved fiber photometry with a single tapered optical fiber implant.

Fiber photometry is increasingly utilized to monitor fluorescent sensors of neural activity in the brain. However, most implementations are based on flat-cleaved optical fibers that can only interface with shallow tissue volumes adjacent to the fiber. We exploit modal properties of tapered optical fibers (TFs) to enable light collection over an extent of up to 2 mm of tissue and multisite photometry along the taper. Using a single TF, we simultaneously observed distinct dopamine transients in dorsal and ventral striatum in freely moving mice performing a simple, operant conditioning task. Collection volumes from TFs can also be engineered in both shape and size by microstructuring the nonplanar surface of the taper, to optically target multiple sites not only in the deep brain but, in general, in any biological system or organ in which light collection is beneficial but challenging because of light scattering and absorption.

Distinct neural mechanisms for reading Arabic vs. verbal numbers: An ERP study.

In this electroencephalogram/event-related potential (EEG/ERP) study, 16 volunteers were asked to compare the numerical equality of 360 pairs of multidigit numbers presented in Arabic or verbal format. Behavioural data showed faster and more accurate responses for digit targets, with a right hand/left hemisphere advantage only for verbal numerals. Occipito-temporal N1, peaking at approximately 180 ms, was strongly left-lateralized during verbal number processing and bilateral during digit processing. A LORETA (low-resolution electromagnetic tomography) source reconstruction performed at the N1 latency stage (155-185 ms) revealed greater brain activation during coding of Arabic than of verbal stimuli. Digit perceptual coding was associated with the activation of the right angular gyrus (rAG), the left fusiform gyrus (FG,BA37), and left and right superior and medial frontal areas. N1 sources for verbal numerals included the left FG (BA37), the precuneus (BA31), the parahippocampal area and a small right prefrontal activation. In addition, verbal numerals elicited a late frontocentral negativity, possibly reflecting stimulus unfamiliarity or complexity. Overall, the data suggest distinct mechanisms for number reading through ciphers (digits) or words. Information about quantity was accessed earlier and more accurately if numbers were in a nonlinguistic code. Indeed, it can be speculated that numerosity processing would involve circuits originally involved in processing space (i.e., rAG/rIPS).

Two-photon fluorescence-assisted laser ablation of non-planar metal surfaces: fabrication of optical apertures on tapered fibers for optical neural interfaces.

We propose a feedback-assisted direct laser writing method to perform laser ablation of fiber optic devices in which their light-collection signal is used to optimize their properties. A femtosecond-pulsed laser beam is used to ablate a metal coating deposited around a tapered optical fiber, employed to show the suitability of the approach to pattern devices with a small radius of curvature. During processing, the same pulses generate two-photon fluorescence in the surrounding environment and the signal is monitored to identify different patterning regimes over time through spectral analysis. The employed fs beam mostly interacts with the metal coating, leaving almost intact the underlying silica and enabling fluorescence to couple with a specific subset of guided modes, as verified by far-field analysis. Although the method is described here for tapered optical fibers used to obtain efficient light collection in the field of optical neural interfaces, it can be easily extended to other waveguide-based devices and represents a general approach to support the implementation of a closed-loop laser ablation system of fiber optics.

Ray tracing models for estimating light collection properties of microstructured tapered optical fibers for optical neural interfaces.

Tapered optical fibers (TFs) were recently employed for depth-resolved monitoring of functional fluorescence in subcortical brain structures, enabling light collection from groups of a few cells through small optical windows located on the taper edge [Pisano et al., Nat. Methods16, 1185 (2019)1548-709110.1038/s41592-019-0581-x]. Here we present a numerical model to estimate light collection properties of microstructured TFs implanted in scattering brain tissue. Ray tracing coupled with the Henyey-Greenstein scattering model enables the estimation of both light collection and fluorescence excitation fields in three dimensions, whose combination is employed to retrieve the volume of tissue probed by the device.

Physical fitness trend after COVID-19 restrictions in Italian school-aged children: a cross-sectional study.

BACKGROUND: Physical fitness (PF) is a marker of health in children. Muscular strength and speed-agility PF components play a crucial role in musculoskeletal development and bone health. The outbreaks of COVID-19 pandemic changed the daily and sports activities in younger increasing sedentary habits with a detrimental effect on PF. We aimed to investigate the impact of COVID-19 restrictions on PF in Italian school-aged children. METHODS: We recruited 286 elementary school children, and they were tested through an internationally validated battery test, which evaluate muscular strength and speed-agility (as a multifactorial performance) prior (2018) and after the outbreak of COVID-19 pandemic (2021). RESULTS: Our results showed a reduction in the lower limb strength (SBJ in boys mean difference (MD) -0.42 m; SBJ in girls MD=-0.20 m; P<0.05) and in the speed-agility ability (10x5 m in boys MD=14.1 s; 10x5 m in girls MD=11.2 s; P<0.05), while the upper limb strength remained steady before and after the restrictions. Specifically, for boys of all ages there was a reduction in lower limb strength and in speed-agility but not in upper limb strength. For girls of all ages there was not a recurrent trend, while for 6-8 girls there was a reduction only speed-agility, for 9-11 girls there was a reduction in lower limb and speed-agility. CONCLUSIONS: Our results could be useful to help teachers and sport specialists to evaluate and improve strength and speed-agility in children. We encourage trainers and sport specialists to implement programs to help children to become more active and healthier during their lifespan.

Self-Declared Physical Activity Levels and Self-Reported Physical Fitness in a Sample of Italian Adolescents during the COVID-19 Pandemic.

Only 20% of children worldwide reach the suggested physical activity (PA) levels, and the COVID-19 restrictions seemed to have worsened this situation. In addition, physical fitness (PF) is a crucial marker of health and combined with PA could predict future health status. The aim of this study was to compare reported PA and PF levels in a sample of Italian adolescents. We administered the International PA Questionnaire and International Fitness Enjoyment Scale to 208 adolescents aged 16.0 ± 1.5 (N = 166 females, 16 ± 2.0 years) recruited from a high school in the province of Milan (Italy). The majority of the subjects were "Minimally active" but reported adequate PF levels. In particular, subjects who reported a "Very good" PF perception, had a lower PA level. The misperception of reported PA and PF from our sample could reduce the future PA level in adolescents and lead to a negative spiral of disengagement in PA. These findings should lead to more attention on and improvements to PA promotion in the adolescent population after the restrictions caused by the COVID-19 pandemic.

Orthogonalization of far-field detection in tapered optical fibers for depth-selective fiber photometry in brain tissue.

The field of implantable optical neural interfaces has recently enabled the interrogation of neural circuitry with both cell-type specificity and spatial resolution in sub-cortical structures of the mouse brain. This generated the need to integrate multiple optical channels within the same implantable device, motivating the requirement of multiplexing and demultiplexing techniques. In this article, we present an orthogonalization method of the far-field space to introduce mode-division demultiplexing for collecting fluorescence from the implantable tapered optical fibers. This is achieved by exploiting the correlation between the transversal wavevector k t of the guided light and the position of the fluorescent sources along the implant, an intrinsic property of the taper waveguide. On these bases, we define a basis of orthogonal vectors in the Fourier space, each of which is associated with a depth along the taper, to simultaneously detect and demultiplex the collected signal when the probe is implanted in fixed mouse brain tissue. Our approach complements the existing multiplexing techniques used in silicon-based photonics probes with the advantage of a significant simplification of the probe itself.

Comparative study of autofluorescence in flat and tapered optical fibers towards application in depth-resolved fluorescence lifetime photometry in brain tissue.

As the scientific community seeks efficient optical neural interfaces with sub-cortical structures of the mouse brain, a wide set of technologies and methods is being developed to monitor cellular events through fluorescence signals generated by genetically encoded molecules. Among these technologies, tapered optical fibers (TFs) take advantage of the modal properties of narrowing waveguides to enable both depth-resolved and wide-volume light collection from scattering tissue, with minimized invasiveness with respect to standard flat fiber stubs (FFs). However, light guided in patch cords as well as in FFs and TFs can result in autofluorescence (AF) signal, which can act as a source of time-variable noise and limit their application to probe fluorescence lifetime in vivo. In this work, we compare the AF signal of FFs and TFs, highlighting the influence of the cladding composition on AF generation. We show that the autofluorescence signal generated in TFs has a peculiar coupling pattern with guided modes, and that far-field detection can be exploited to separate functional fluorescence from AF. On these bases, we provide evidence that TFs can be employed to implement depth-resolved fluorescence lifetime photometry, potentially enabling the extraction of a new set of information from deep brain regions, as time-correlating single photon counting starts to be applied in freely-moving animals to monitor the intracellular biochemical state of neurons.

Influence of the anatomical features of different brain regions on the spatial localization of fiber photometry signals.

Fiber photometry is widely used in neuroscience labs for in vivo detection of functional fluorescence from optical indicators of neuronal activity with a simple optical fiber. The fiber is commonly placed next to the region of interest to both excite and collect the fluorescence signal. However, the path of both excitation and fluorescence photons is altered by the uneven optical properties of the brain, due to local variation of the refractive index, different cellular types, densities and shapes. Nonetheless, the effect of the local anatomy on the actual shape and extent of the volume of tissue that interfaces with the fiber has received little attention so far. To fill this gap, we measured the size and shape of fiber photometry efficiency field in the primary motor and somatosensory cortex, in the hippocampus and in the striatum of the mouse brain, highlighting how their substructures determine the detected signal and the depth at which photons can be mined. Importantly, we show that the information on the spatial expression of the fluorescent probes alone is not sufficient to account for the contribution of local subregions to the overall collected signal, and it must be combined with the optical properties of the tissue adjacent to the fiber tip.

Does reactivity to accelerometers occur in a single trial? Brief report in a sample of young adults.

This study aimed to test acute reactivity during a physical activity in an outdoor setting and to verify the relative perceived performance. In all, 38 volunteers wore accelerometers or not and completed two 20-minute sessions of self-selected pace physical activity. Covered distance, exertional responses, and perceived efficacy were recorded at the end of every session. Relevant finding of this study has been that reactivity to accelerometers also occurs in acute condition. Consequently, this condition leads to a better performance and a greater perceived exertion. Moreover, this situation seems to occur in a state of awareness.