Cortical cross-modal plasticity following deafness measured using functional near-infrared spectroscopy

Evidence from functional neuroimaging studies suggests that the auditory cortex can become more responsive to visual and somatosensory stimulation following deafness, and that this occurs predominately in the right hemisphere. Extensive cross-modal plasticity in prospective cochlear implant recipients is correlated with poor speech outcomes following implantation, highlighting the potential impact of central auditory plasticity on subsequent aural rehabilitation. Conversely, the effects of hearing restoration with a cochlear implant on cortical plasticity are less well understood, since the use of most neuroimaging techniques in CI recipients is either unsafe or problematic due to the electromagnetic artefacts generated by CI stimulation. Additionally, techniques such as functional magnetic resonance imaging (fMRI) are confounded by acoustic noise produced by the scanner that will be perceived more by hearing than by deaf individuals. Subsequently it is conceivable that auditory responses to acoustic noise produced by the MR scanner may mask auditory cortical responses to non-auditory stimulation, and render inter-group comparisons less significant. Uniquely, functional near-infrared spectroscopy (fNIRS) is a silent neuroimaging technique that is non-invasive and completely unaffected by the presence of a CI. Here, we used fNIRS to study temporal-lobe responses to auditory, visual and somatosensory stimuli in thirty profoundly-deaf participants and thirty normally-hearing controls. Compared with silence, acoustic noise stimuli elicited a significant group fNIRS response in the temporal region of normally-hearing individuals, which was not seen in profoundly-deaf participants. Visual motion elicited a larger group response within the right temporal lobe of profoundly-deaf participants, compared with normally-hearing controls. However, bilateral temporal lobe fNIRS activation to somatosensory stimulation was comparable in both groups. Using fNIRS these results confirm that auditory deprivation is associated with cross-modal plasticity of visual inputs to auditory cortex. Although we found no evidence for plasticity of somatosensory inputs, it is possible that our recordings may have included activation of somatosensory cortex that masked any group differences in auditory cortical responses due to the limited spatial resolution associated with fNIRS

How getting the right actors involved can help successful local policies spread across the country

One of the oft-cited advantages of the US system of government is that it gives state and local governments the ability to innovate in policymaking. But how can policies which are successful in one area be taken up elsewhere? In new research which examines the introduction by states of drug courts for non-violent offenders, James W. Douglas, Ringa Raudla, and Roger E. Hartley write that the spread of such policies is influenced by other governments who have already adopted the policy, state and local governments, and professional, national, and regional associations and lobby groups. Without the support of such key actors, they write, successful local policy innovations are unlikely to spread widely

Brain activity underlying the recovery of meaning from degraded speech: a functional near-infrared spectroscopy (fNIRS) study

The purpose of this study was to establish whether functional near-infrared spectroscopy (fNIRS), an emerging brain-imaging technique based on optical principles, is suitable for studying the brain activity that underlies effortful listening. In an event-related fNIRS experiment, normally-hearing adults listened to sentences that were either clear or degraded (noise vocoded). These sentences were presented simultaneously with a non-speech distractor, and on each trial participants were instructed to attend either to the speech or to the distractor. The primary region of interest for the fNIRS measurements was the left inferior frontal gyrus (LIFG), a cortical region involved in higher-order language processing. The fNIRS results confirmed findings previously reported in the functional magnetic resonance imaging (fMRI) literature. Firstly, the LIFG exhibited an elevated response to degraded versus clear speech, but only when attention was directed towards the speech. This attention-dependent increase in frontal brain activation may be a neural marker for effortful listening. Secondly, during attentive listening to degraded speech, the haemodynamic response peaked significantly later in the LIFG than in superior temporal cortex, possibly reflecting the engagement of working memory to help reconstruct the meaning of degraded sentences. The homologous region in the right hemisphere may play an equivalent role to the LIFG in some left-handed individuals. In conclusion, fNIRS holds promise as a flexible tool to examine the neural signature of effortful listening

Ecological aspects of vegetation establishment on landfills.

Thesis (Ph.D.)-University of Natal, Durban, 2003.A high level of plant mortality on the Bisasar Road landfill, Durban, South Africa initiated an investigation into the primary causes of the mortalities and a search for potentially tolerant plant species. Field studies revealed that volunteer grass growth on cover soils was primarily limited by elevated soil C02, with high soil conductivity and low soil moisture possibly compounding the effect. Cynodon dactylon, the most abundant coloniser of the site appeared to be relatively sensitive to high soil CO2, whilst less common species such as Sporobolis cifricanus and Paspalum Paspoloides appeared to be less sensitive. Further research focused on the high mortality of trees planted on the landfill providing insight into the important variables limiting survival· and the relative differences in performance of 20 tree species. A more rigorous 14-month field experiment was designed and constructed, to assess the performance of 10 of the more promising tree species, the environmental conditions limiting tree growth and the benefit of a deeper layer of better quality topsoil. Some species, such as Barringtonia racemosa, performed relatively well in the field experiment, whilst other species such as Syzygium cordatum, and Harpephyllum caffrom experienced high mortalities and poor growth. The better quality topsoil layer provided little improvement in the performance of the stronger or the weaker species, however significant improvements were recorded for species with relatively intermediate performance. The composition of the soil atmosphere was shown to determine rooting depth. Species that performed better had deeper roots, possibly assisting them in utilising deeper soil moisture reserves. It was concluded that high soil CO2 and low soil O2 levels were the key variables responsible for poor tree survival and growth in this field experiment. A soil fumigation system was designed to provide more control of soil gas concentrations and to experimentally investigate differential species responses and the relative effects of soil CO2 and O2 on tree survival and growth. The apparatus fumigated, for a period of 140 days, the rhizosphere of 80 potted 'tolerant' (Barringtonia racemosa) and 'non tolerant' (Harpephyllum caffrum) trees with 4 treatments consisting of varying combinations of CO2 and 02. The difference in performance of Barringtonia racemosa and Harpephyllum caffrum in the experiment on the landfill was similar to that of the elevated CO2 low O2 fumigation treatment, supporting the premise that landfill gas was the key cause for poor performance of plants. Reduced stomatal conductance and resultant limitations on photosynthesis were found to be indicative of species sensitivity. Low O2 had an additive effect on the impact of elevated CO2 in Harpephyllum caffrum however, even with normal soil O2 levels, 25% soil CO2 had negative growth effects on this sensitive species. Maintenance of plant health and better performance of Barringtonia was attributed to a high inherent level of tissue porosity and aerenchyma. The research provided a greater understanding of the causes of poor vegetation growth and the possible mechanisms of species tolerance to landfill conditions

Spirality: A Novel Way to Measure Spiral Arm Pitch Angle

We present the MATLAB code Spirality, a novel method for measuring spiral arm pitch angles by fitting galaxy images to spiral templates of known pitch. Computation time is typically on the order of 2 minutes per galaxy, assuming at least 8 GB of working memory. We tested the code using 117 synthetic spiral images with known pitches, varying both the spiral properties and the input parameters. The code yielded correct results for all synthetic spirals with galaxy-like properties. We also compared the code's results to two-dimensional Fast Fourier Transform (2DFFT) measurements for the sample of nearby galaxies defined by DMS PPak. Spirality's error bars overlapped 2DFFT's error bars for 26 of the 30 galaxies. The two methods' agreement correlates strongly with galaxy radius in pixels and also with i-band magnitude, but not with redshift, a result that is consistent with at least some galaxies' spiral structure being fully formed by z=1.2, beyond which there are few galaxies in our sample. The Spirality code package also includes GenSpiral, which produces FITS images of synthetic spirals, and SpiralArmCount, which uses a one-dimensional Fast Fourier Transform to count the spiral arms of a galaxy after its pitch is determined. The code package is freely available online; see Comments for URL.Comment: 19 pages, 9 figures, 3 tables. The code package is available at http://dafix.uark.edu/~doug/SpiralityCode

A synchrony-dependent influence of sounds on activity in visual cortex measured using functional near-infrared spectroscopy (fNIRS)

Evidence from human neuroimaging and animal electrophysiological studies suggests that signals from different sensory modalities interact early in cortical processing, including in primary sensory cortices. The present study aimed to test whether functional near-infrared spectroscopy (fNIRS), an emerging, non-invasive neuroimaging technique, is capable of measuring such multisensory interactions. Specifically, we tested for a modulatory influence of sounds on activity in visual cortex, while varying the temporal synchrony between trains of transient auditory and visual events. Related fMRI studies have consistently reported enhanced activation in response to synchronous compared to asynchronous audiovisual stimulation. Unexpectedly, we found that synchronous sounds significantly reduced the fNIRS response from visual cortex, compared both to asynchronous sounds and to a visual-only baseline. It is possible that this suppressive effect of synchronous sounds reflects the use of an efficacious visual stimulus, chosen for consistency with previous fNIRS studies. Discrepant results may also be explained by differences between studies in how attention was deployed to the auditory and visual modalities. The presence and relative timing of sounds did not significantly affect performance in a simultaneously conducted behavioral task, although the data were suggestive of a positive relationship between the strength of the fNIRS response from visual cortex and the accuracy of visual target detection. Overall, the present findings indicate that fNIRS is capable of measuring multisensory cortical interactions. In multisensory research, fNIRS can offer complementary information to the more established neuroimaging modalities, and may prove advantageous for testing in naturalistic environments and with infant and clinical populations

Shedding Light On The Human Auditory Cortex: A Review Of The Advances In Near Infrared Spectroscopy (NIRS)

Imaging the auditory cortex can prove challenging using neuroimaging methodologies due to interfering noise from the scanner in fMRI and the low spatial resolution of EEG. Optical imaging provides a new and exciting option for exploring this key cortical area. This review presents a brief history of optical imaging, followed by an exploration of how advances in optical imaging technologies have increased the understanding of the functions and processes within the auditory cortex. In particular, the benefits and limitations of using functional near infrared spectroscopy (fNIRS) on complex populations such as infants and individuals with hearing loss are explored, along with suggestions for future research developments

Multisensory Training Improves Auditory Spatial Processing following Bilateral Cochlear Implantation

Cochlear implants (CIs) partially restore hearing to the deaf by directly stimulating the inner ear. In individuals fitted with CIs, lack of auditory experience due to loss of hearing before language acquisition can adversely impact outcomes. For example, adults with early-onset hearing loss generally do not integrate inputs from both ears effectively when fitted with bilateral CIs (BiCIs). Here, we used an animal model to investigate the effects of long-term deafness on auditory localization with BiCIs and approaches for promoting the use of binaural spatial cues. Ferrets were deafened either at the age of hearing onset or as adults. All animals were implanted in adulthood, either unilaterally or bilaterally, and were subsequently assessed for their ability to localize sound in the horizontal plane. The unilaterally implanted animals were unable to perform this task, regardless of the duration of deafness. Among animals with BiCIs, early-onset hearing loss was associated with poor auditory localization performance, compared with late-onset hearing loss. However, performance in the early-deafened group with BiCIs improved significantly after multisensory training with interleaved auditory and visual stimuli. We demonstrate a possible neural substrate for this by showing a training-induced improvement in the responsiveness of auditory cortical neurons and in their sensitivity to interaural level differences, the principal localization cue available to BiCI users. Importantly, our behavioral and physiological evidence demonstrates a facilitative role for vision in restoring auditory spatial processing following potential cross-modal reorganization. These findings support investigation of a similar training paradigm in human CI users

Envelope enhancement increases cortical sensitivity to interaural envelope delays with acoustic and electric hearing

Evidence from human psychophysical and animal electrophysiological studies suggests that sensitivity to interaural time delay (ITD) in the modulating envelope of a high-frequency carrier can be enhanced using half-wave rectified stimuli. Recent evidence has shown potential benefits of equivalent electrical stimuli to deaf individuals with bilateral cochlear implants (CIs). In the current study we assessed the effects of envelope shape on ITD sensitivity in the primary auditory cortex of normal-hearing ferrets, and profoundly-deaf animals with bilateral CIs. In normal-hearing animals, cortical sensitivity to ITDs (±1 ms in 0.1-ms steps) was assessed in response to dichotically-presented i) sinusoidal amplitude-modulated (SAM) and ii) half-wave rectified (HWR) tones (100-ms duration; 70 dB SPL) presented at the best-frequency of the unit over a range of modulation frequencies. In separate experiments, adult ferrets were deafened with neomycin administration and bilaterally-implanted with intra-cochlear electrode arrays. Electrically-evoked auditory brainstem responses (EABRs) were recorded in response to bipolar electrical stimulation of the apical pair of electrodes with singe biphasic current pulses (40 µs per phase) over a range of current levels to measure hearing thresholds. Subsequently, we recorded cortical sensitivity to ITDs (±800 µs in 80-µs steps) within the envelope of SAM and HWR biphasic-pulse trains (40 µs per phase; 6000 pulses per second, 100-ms duration) over a range of modulation frequencies. In normal-hearing animals, nearly a third of cortical neurons were sensitive to envelope-ITDs in response to SAM tones. In deaf animals with bilateral CI, the proportion of ITD-sensitive cortical neurons was approximately a fifth in response to SAM pulse trains. In normal-hearing and deaf animals with bilateral CI the proportion of ITD sensitive units and neural sensitivity to ITDs increased in response to HWR, compared with SAM stimuli. Consequently, novel stimulation strategies based on envelope enhancement may prove beneficial to individuals with bilateral cochlear implants