Effect of Elevated Intracranial Pressure on Amplitudes and Frequency Tuning of Ocular Vestibular Evoked Myogenic Potentials Elicited by Bone-Conducted Vibration.

Objective: Recently, it could be demonstrated that an increased intracranial pressure causes a modulation of the air conducted sound evoked ocular vestibular evoked myogenic potential (oVEMP). The mechanism for this modulation is not resolved and may depend on a change of either receptor excitability or sound energy transmission. Design: oVEMPs were elicited in 18 healthy subjects with a minishaker delivering 500 and 1000 Hz tone bursts, in supine and tilted positions. Results: The study could confirm the frequency tuning of oVEMP. However, at neither stimulus frequency could a modulating effect of increased intracranial pressure be observed. Conclusion: These data suggest that the observed modulation of the oVEMP response by an increased intracranial pressure is primarily due to the effect of an increased intralabyrinthine pressure onto the stiffness of the inner ear contents and the middle ear-inner ear junction. Future studies on the effect of intracranial pressure on oVEMP should use air-conducted sound and not bone-conducted vibration. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.

from #Audiology via ola Kala on Inoreader http://ift.tt/2agCKwO
via IFTTT

Effect of Elevated Intracranial Pressure on Amplitudes and Frequency Tuning of Ocular Vestibular Evoked Myogenic Potentials Elicited by Bone-Conducted Vibration.

Objective: Recently, it could be demonstrated that an increased intracranial pressure causes a modulation of the air conducted sound evoked ocular vestibular evoked myogenic potential (oVEMP). The mechanism for this modulation is not resolved and may depend on a change of either receptor excitability or sound energy transmission. Design: oVEMPs were elicited in 18 healthy subjects with a minishaker delivering 500 and 1000 Hz tone bursts, in supine and tilted positions. Results: The study could confirm the frequency tuning of oVEMP. However, at neither stimulus frequency could a modulating effect of increased intracranial pressure be observed. Conclusion: These data suggest that the observed modulation of the oVEMP response by an increased intracranial pressure is primarily due to the effect of an increased intralabyrinthine pressure onto the stiffness of the inner ear contents and the middle ear-inner ear junction. Future studies on the effect of intracranial pressure on oVEMP should use air-conducted sound and not bone-conducted vibration. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.

from #Audiology via ola Kala on Inoreader http://ift.tt/2agCKwO
via IFTTT

Effect of Elevated Intracranial Pressure on Amplitudes and Frequency Tuning of Ocular Vestibular Evoked Myogenic Potentials Elicited by Bone-Conducted Vibration.

Objective: Recently, it could be demonstrated that an increased intracranial pressure causes a modulation of the air conducted sound evoked ocular vestibular evoked myogenic potential (oVEMP). The mechanism for this modulation is not resolved and may depend on a change of either receptor excitability or sound energy transmission. Design: oVEMPs were elicited in 18 healthy subjects with a minishaker delivering 500 and 1000 Hz tone bursts, in supine and tilted positions. Results: The study could confirm the frequency tuning of oVEMP. However, at neither stimulus frequency could a modulating effect of increased intracranial pressure be observed. Conclusion: These data suggest that the observed modulation of the oVEMP response by an increased intracranial pressure is primarily due to the effect of an increased intralabyrinthine pressure onto the stiffness of the inner ear contents and the middle ear-inner ear junction. Future studies on the effect of intracranial pressure on oVEMP should use air-conducted sound and not bone-conducted vibration. Copyright (C) 2016 Wolters Kluwer Health, Inc. All rights reserved.

from #Audiology via xlomafota13 on Inoreader http://ift.tt/2agCKwO
via IFTTT

Continuing the Unique Journey - New Products in the Widex Unique Family

Widex believes that every patient in every situation is absolutely unique: hence, the name Widex UNIQUE. On a daily basis, patients explain to us the settings in which they would like to hear better and where they are struggling. Everyone has different lifestyles, family dynamics, and a myriad of activities that they enjoy. With the UNIQUE product line, Widex has designed hearing aids to fit and to be appropriate for as many people in as many situations as possible.

from #Audiology via xlomafota13 on Inoreader http://ift.tt/2aAze0h
via IFTTT

Continuing the Unique Journey - New Products in the Widex Unique Family

Widex believes that every patient in every situation is absolutely unique: hence, the name Widex UNIQUE. On a daily basis, patients explain to us the settings in which they would like to hear better and where they are struggling. Everyone has different lifestyles, family dynamics, and a myriad of activities that they enjoy. With the UNIQUE product line, Widex has designed hearing aids to fit and to be appropriate for as many people in as many situations as possible.

from #Audiology via ola Kala on Inoreader http://ift.tt/2aAze0h
via IFTTT

Continuing the Unique Journey - New Products in the Widex Unique Family

Widex believes that every patient in every situation is absolutely unique: hence, the name Widex UNIQUE. On a daily basis, patients explain to us the settings in which they would like to hear better and where they are struggling. Everyone has different lifestyles, family dynamics, and a myriad of activities that they enjoy. With the UNIQUE product line, Widex has designed hearing aids to fit and to be appropriate for as many people in as many situations as possible.

from #Audiology via ola Kala on Inoreader http://ift.tt/2aAze0h
via IFTTT

Recovery of ambulation activity across the first six months post-stroke

Publication date: September 2016
Source:Gait & Posture, Volume 49
Author(s): Niruthikha Mahendran, Suzanne S. Kuys, Sandra G. Brauer
Stroke survivors commonly adopt sedentary activity behaviours by the chronic phase of recovery. However, the change in activity behaviours from the subacute to chronic phase of stroke is variable. This study explored the recovery of ambulation activity (volume and bouts) at one, three and six months after hospital discharge post-stroke. A total of 42 stroke survivors were recruited at hospital discharge and followed up one, three and six months later. At follow-up, ambulation activity was measured over four days using the ActivPAL™ accelerometer. Measures included volume of activity and frequency and intensity of ambulation activity bouts per day. Linear mixed effects modelling was used to determine changes over time. There was wide variation in activity. Total step counts across all time points were below required levels for health benefits (mean 4592 SD 3411). Most activity was spread across short bouts. While most number of bouts was of low intensity, most time was spent in moderate intensity ambulation across all time points. Daily step count and time spent walking and sitting/lying increased from one month to three and six months. The number of and time spent in short and medium duration bouts increased from one to six months. Time in long duration bouts increased at three months only. Time spent in moderate intensity ambulation increased over time. No change was observed for any other measures. In future, it would be valuable to identify strategies to increase engagement in activity behaviours to improve health outcomes after stroke.



from #Audiology via xlomafota13 on Inoreader http://ift.tt/2ak2xyX
via IFTTT

Recovery of ambulation activity across the first six months post-stroke

Publication date: September 2016
Source:Gait & Posture, Volume 49
Author(s): Niruthikha Mahendran, Suzanne S. Kuys, Sandra G. Brauer
Stroke survivors commonly adopt sedentary activity behaviours by the chronic phase of recovery. However, the change in activity behaviours from the subacute to chronic phase of stroke is variable. This study explored the recovery of ambulation activity (volume and bouts) at one, three and six months after hospital discharge post-stroke. A total of 42 stroke survivors were recruited at hospital discharge and followed up one, three and six months later. At follow-up, ambulation activity was measured over four days using the ActivPAL™ accelerometer. Measures included volume of activity and frequency and intensity of ambulation activity bouts per day. Linear mixed effects modelling was used to determine changes over time. There was wide variation in activity. Total step counts across all time points were below required levels for health benefits (mean 4592 SD 3411). Most activity was spread across short bouts. While most number of bouts was of low intensity, most time was spent in moderate intensity ambulation across all time points. Daily step count and time spent walking and sitting/lying increased from one month to three and six months. The number of and time spent in short and medium duration bouts increased from one to six months. Time in long duration bouts increased at three months only. Time spent in moderate intensity ambulation increased over time. No change was observed for any other measures. In future, it would be valuable to identify strategies to increase engagement in activity behaviours to improve health outcomes after stroke.



from #Audiology via ola Kala on Inoreader http://ift.tt/2ak2xyX
via IFTTT

Recovery of ambulation activity across the first six months post-stroke

Publication date: September 2016
Source:Gait & Posture, Volume 49
Author(s): Niruthikha Mahendran, Suzanne S. Kuys, Sandra G. Brauer
Stroke survivors commonly adopt sedentary activity behaviours by the chronic phase of recovery. However, the change in activity behaviours from the subacute to chronic phase of stroke is variable. This study explored the recovery of ambulation activity (volume and bouts) at one, three and six months after hospital discharge post-stroke. A total of 42 stroke survivors were recruited at hospital discharge and followed up one, three and six months later. At follow-up, ambulation activity was measured over four days using the ActivPAL™ accelerometer. Measures included volume of activity and frequency and intensity of ambulation activity bouts per day. Linear mixed effects modelling was used to determine changes over time. There was wide variation in activity. Total step counts across all time points were below required levels for health benefits (mean 4592 SD 3411). Most activity was spread across short bouts. While most number of bouts was of low intensity, most time was spent in moderate intensity ambulation across all time points. Daily step count and time spent walking and sitting/lying increased from one month to three and six months. The number of and time spent in short and medium duration bouts increased from one to six months. Time in long duration bouts increased at three months only. Time spent in moderate intensity ambulation increased over time. No change was observed for any other measures. In future, it would be valuable to identify strategies to increase engagement in activity behaviours to improve health outcomes after stroke.



from #Audiology via ola Kala on Inoreader http://ift.tt/2ak2xyX
via IFTTT

Collagen type IV-related nephropathies in Portugal: pathogenic COL4A3 and COL4A4 mutations and clinical characterization of 25 families.

Related Articles

Collagen type IV-related nephropathies in Portugal: pathogenic COL4A3 and COL4A4 mutations and clinical characterization of 25 families.

Clin Genet. 2015 Nov;88(5):456-61

Authors: Nabais Sá MJ, Storey H, Flinter F, Nagel M, Sampaio S, Castro R, Araújo JA, Gaspar MA, Soares C, Oliveira A, Henriques AC, da Costa AG, Abreu CP, Ponce P, Alves R, Pinho L, Silva SE, de Moura CP, Mendonça L, Carvalho F, Pestana M, Alves S, Carvalho F, Oliveira JP

Abstract
Pathogenic mutations in genes COL4A3/COL4A4 are responsible for autosomal Alport syndrome (AS) and thin basement membrane nephropathy (TBMN). We used Sanger sequencing to analyze all exons and splice site regions of COL4A3/COL4A4, in 40 unrelated Portuguese probands with clinical suspicion of AS/TBMN. To assess genotype-phenotype correlations, we compared clinically relevant phenotypes/outcomes between homozygous/compound heterozygous and apparently heterozygous patients. Seventeen novel and four reportedly pathogenic COL4A3/COL4A4 mutations were identified in 62.5% (25/40) of the probands. Regardless of the mutated gene, all patients with ARAS manifested chronic renal failure (CRF) and hearing loss, whereas a minority of the apparently heterozygous patients had CRF or extrarenal symptoms. CRF was diagnosed at a significantly younger age in patients with ARAS. In our families, the occurrence of COL4A3/COL4A4 mutations was higher, while the prevalence of XLAS was lower than expected. Overall, a pathogenic COL4A3/COL4A4/COL4A5 mutation was identified in >50% of patients with fewer than three of the standard diagnostic criteria of AS. With such a population background, simultaneous next-generation sequencing of all three genes may be recommended as the most expedite approach to diagnose collagen IV-related glomerular basement membrane nephropathies.

PMID: 25307543 [PubMed - indexed for MEDLINE]

from #Audiology via xlomafota13 on Inoreader http://ift.tt/2aA6hOF
via IFTTT

Growth rate of vestibular schwannoma.

Related Articles

Growth rate of vestibular schwannoma.

J Clin Neurosci. 2016 Jul 20;

Authors: Paldor I, Chen AS, Kaye AH

Abstract
Vestibular schwannoma (VS) is the most common tumor in the extra-axial posterior fossa compartment in adults. Growth rate is paramount to decision making regarding treatment and follow up of these tumors. We conducted a comprehensive review of the literature to answer four questions: What percentage of newly diagnosed VS will grow on follow-up? What factors correlate to tumor growth? What is the "normal" growth rate for sporadic VS? What factors characterize VS with rapid growth? Thirty-seven reports, with more than 4000 patients, fit our review criteria. One third of newly diagnosed VS will grow on follow-up of 1-3years. However, after 5years, up to one half will grow. Patient age and sex do not influence growth of VS. Hearing loss and vertigo at presentation do not predict tumor growth. It is unclear whether balance disturbance or tinnitus predict tumor growth. Tumor size and location do not predict tumor growth. Growth in the first year of observation is a strong predictor of tumor growth. The average growth rate of a VS is 0.99-1.11mm/year. However, the expected growth rate for VS that have been shown to grow at first follow-up is 3mm/year. Factors that may predict tumor growth of above 4mm/year are cystic and hemorrhagic features in the tumor, and hormonal treatment. VS grow at an average 1mm/year. VS that have been shown to grow at first follow-up should be considered for treatment, unless contraindicated. Long term follow-up is recommended for VS.

PMID: 27450283 [PubMed - as supplied by publisher]

from #Audiology via ola Kala on Inoreader http://ift.tt/2adZptZ
via IFTTT

Growth rate of vestibular schwannoma.

Related Articles

Growth rate of vestibular schwannoma.

J Clin Neurosci. 2016 Jul 20;

Authors: Paldor I, Chen AS, Kaye AH

Abstract
Vestibular schwannoma (VS) is the most common tumor in the extra-axial posterior fossa compartment in adults. Growth rate is paramount to decision making regarding treatment and follow up of these tumors. We conducted a comprehensive review of the literature to answer four questions: What percentage of newly diagnosed VS will grow on follow-up? What factors correlate to tumor growth? What is the "normal" growth rate for sporadic VS? What factors characterize VS with rapid growth? Thirty-seven reports, with more than 4000 patients, fit our review criteria. One third of newly diagnosed VS will grow on follow-up of 1-3years. However, after 5years, up to one half will grow. Patient age and sex do not influence growth of VS. Hearing loss and vertigo at presentation do not predict tumor growth. It is unclear whether balance disturbance or tinnitus predict tumor growth. Tumor size and location do not predict tumor growth. Growth in the first year of observation is a strong predictor of tumor growth. The average growth rate of a VS is 0.99-1.11mm/year. However, the expected growth rate for VS that have been shown to grow at first follow-up is 3mm/year. Factors that may predict tumor growth of above 4mm/year are cystic and hemorrhagic features in the tumor, and hormonal treatment. VS grow at an average 1mm/year. VS that have been shown to grow at first follow-up should be considered for treatment, unless contraindicated. Long term follow-up is recommended for VS.

PMID: 27450283 [PubMed - as supplied by publisher]

from #Audiology via ola Kala on Inoreader http://ift.tt/2adZptZ
via IFTTT

Capturing contextual effects in spectro-temporal receptive fields

Publication date: Available online 27 July 2016
Source:Hearing Research
Author(s): Johan Westö, Patrick J.C. May
Spectro-temporal receptive fields (STRFs) are thought to provide descriptive images of the computations performed by neurons along the auditory pathway. However, their validity can be questioned because they rely on a set of assumptions that are probably not fulfilled by real neurons exhibiting contextual effects, that is, nonlinear interactions in the time or frequency dimension that cannot be described with a linear filter. We used a novel approach to investigate how a variety of contextual effects, due to facilitating nonlinear interactions and synaptic depression, affect different STRF models, and if these effects can be captured with a context field (CF). Contextual effects were incorporated in simulated networks of spiking neurons, allowing one to define the true STRFs of the neurons. This, in turn, made it possible to evaluate the performance of each STRF model by comparing the estimations with the true STRFs. We found that currently used STRF models are particularly poor at estimating inhibitory regions. Specifically, contextual effects make estimated STRFs dependent on stimulus density in a contrasting fashion: inhibitory regions are underestimated at lower densities while artificial inhibitory regions emerge at higher densities. The CF was found to provide a solution to this dilemma, but only when it is used together with a generalized linear model. Our results therefore highlight the limitations of the traditional STRF approach and provide useful recipes for how different STRF models and stimuli can be used to arrive at reliable quantifications of neural computations in the presence of contextual effects. The results therefore push the purpose of STRF analysis from simply finding an optimal stimulus toward describing context-dependent computations of neurons along the auditory pathway.



from #Audiology via xlomafota13 on Inoreader http://ift.tt/2ay3vwF
via IFTTT

Dopamine agonists for preventing future miscarriage in women with idiopathic hyperprolactinemia and recurrent miscarriage history.

Related Articles

Dopamine agonists for preventing future miscarriage in women with idiopathic hyperprolactinemia and recurrent miscarriage history.

Cochrane Database Syst Rev. 2016 Jul 25;7:CD008883

Authors: Chen H, Fu J, Huang W

Abstract
BACKGROUND: Hyperprolactinemia is the presence of abnormally high circulating levels of prolactin. Idopathic hyperprolactinemia is the term used when no cause of prolactin hypersecretion can be identified and it is causally related to the development of miscarriage in pregnant women, especially women who have a history of recurrent miscarriage. A possible mechanism is that high levels of prolactin affect the function of the ovaries, resulting in a luteal phase defect and miscarriage. A dopamine agonist is a compound with high efficacy in lowering prolactin levels and restoring gonadal function.
OBJECTIVES: To assess the effectiveness and safety of different types of dopamine agonists in preventing future miscarriage given to women with idiopathic hyperprolactinemia and a history of recurrent miscarriage.
SEARCH METHODS: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (30 June 2016) and reference lists of retrieved studies.
SELECTION CRITERIA: Randomized controlled trials (RCTs) in all languages examining the effect of dopamine agonists on preventing future miscarriage. Women who had idiopathic hyperprolactinemia with a history of recurrent miscarriages were eligible for inclusion in this review. Comparisons planned included: dopamine agonists alone versus placebo/no treatment; and dopamine agonists combined with other therapy versus other therapy alone.
DATA COLLECTION AND ANALYSIS: Two review authors independently assessed a single trial for inclusion, evaluated trial quality and extracted data. Data were checked for accuracy.
MAIN RESULTS: One study (recruiting 48 women with idiopathic hyperprolactinemia) met our inclusion criteria; 46 women (42 pregnancies - 4/46 women did not conceive during the study period) were included in the analysis. The study compared the use of a dopamine agonist (bromocriptine, 2.5 mg to 5.0 mg/day until the end of the ninth week of gestation) versus a no-treatment control. The study was judged as being at a high risk of bias. It was not possible to carry out meta-analysis due to insufficient data.The study reported both of this review's primary outcomes of miscarriage and live birth. Results from this single study suggest that, compared to no treatment, oral bromocriptine was effective in preventing future miscarriage (risk ratio (RR) 0.28, 95% confidence interval (CI) 0.09 to 0.87, 46 participants (low-quality evidence)) in women with idiopathic hyperprolactinemia. There was no clear difference with regard to the other primary outcome of live births (RR 1.50, 95% CI 0.93 to 2.42, 46 participants (very low-quality evidence)).There was no difference with regard to this review's secondary outcome of conception (RR 0.92, 95% CI 0.77 to 1.09, 46 participants (very low-quality evidence)) between the group of women who received dopamine (21 out of 24 women conceived) and women in the no-treatment group (21 out of 22 women conceived). The included study only reported the serum prolactin levels in pregnant women and therefore the data could not be analyzed in this review. No other secondary outcomes relevant to this review were reported; adverse effects for women (nausea, vomiting, headache, vertigo, fatigue, hypotension, arrhythmia, and psychotic symptoms) and infants (birth defects, low birthweight, and developmental disabilities) were not reported.We downgraded the quality of the evidence for risk of bias in the one trial contributing outcome data (no description of allocation concealment, lack of blinding and possible reporting bias) and for imprecision (all effect estimates were based on small sample size, miscarriage was based on few events, and the 95% CIs of live birth and conception cross the line of no effect).
AUTHORS' CONCLUSIONS: Currently, there is insufficient evidence (from a single randomized trial with a small sample size, and judged to be at high risk of bias) to evaluate the effectiveness of dopamine agonists for preventing future miscarriage in women with idiopathic hyperprolactinemia and a history of recurrent miscarriage. We assessed outcomes using GRADE methodology. Miscarriage was assessed as low quality due to risk of bias concerns in the one trial contributing data (no description of allocation concealment, lack of blinding and possible reporting bias) and to imprecision (effect estimates were based on small sample size and few events). Live births and conception were assessed as of very low quality due to the same risk of bias concerns in study design and to imprecision (with a wide 95% CI consistent with either benefit or harm), and a small sample size. There were no data relating to adverse effects of the intervention for either the mother or her baby.Futher high-quality research in this area is warranted. There is a need for well-designed, larger RCTs to confirm and extend the findings of the trial reviewed here. Many questions remain unanswered. Some important considerations for future research include, the need for well-designed RCTs with large sample sizes, and for those studies to consider important outcomes (including adverse effects for both the mother and her baby). Future studies should examine the effectiveness and safety of various dopamine agonists including bromocriptine, cabergoline and quinagolide.

PMID: 27455388 [PubMed - as supplied by publisher]

from #Audiology via xlomafota13 on Inoreader http://ift.tt/2agCBqF
via IFTTT

Capturing contextual effects in spectro-temporal receptive fields

Publication date: Available online 27 July 2016
Source:Hearing Research
Author(s): Johan Westö, Patrick J.C. May
Spectro-temporal receptive fields (STRFs) are thought to provide descriptive images of the computations performed by neurons along the auditory pathway. However, their validity can be questioned because they rely on a set of assumptions that are probably not fulfilled by real neurons exhibiting contextual effects, that is, nonlinear interactions in the time or frequency dimension that cannot be described with a linear filter. We used a novel approach to investigate how a variety of contextual effects, due to facilitating nonlinear interactions and synaptic depression, affect different STRF models, and if these effects can be captured with a context field (CF). Contextual effects were incorporated in simulated networks of spiking neurons, allowing one to define the true STRFs of the neurons. This, in turn, made it possible to evaluate the performance of each STRF model by comparing the estimations with the true STRFs. We found that currently used STRF models are particularly poor at estimating inhibitory regions. Specifically, contextual effects make estimated STRFs dependent on stimulus density in a contrasting fashion: inhibitory regions are underestimated at lower densities while artificial inhibitory regions emerge at higher densities. The CF was found to provide a solution to this dilemma, but only when it is used together with a generalized linear model. Our results therefore highlight the limitations of the traditional STRF approach and provide useful recipes for how different STRF models and stimuli can be used to arrive at reliable quantifications of neural computations in the presence of contextual effects. The results therefore push the purpose of STRF analysis from simply finding an optimal stimulus toward describing context-dependent computations of neurons along the auditory pathway.



from #Audiology via ola Kala on Inoreader http://ift.tt/2ay3vwF
via IFTTT

Capturing contextual effects in spectro-temporal receptive fields

Publication date: Available online 27 July 2016
Source:Hearing Research
Author(s): Johan Westö, Patrick J.C. May
Spectro-temporal receptive fields (STRFs) are thought to provide descriptive images of the computations performed by neurons along the auditory pathway. However, their validity can be questioned because they rely on a set of assumptions that are probably not fulfilled by real neurons exhibiting contextual effects, that is, nonlinear interactions in the time or frequency dimension that cannot be described with a linear filter. We used a novel approach to investigate how a variety of contextual effects, due to facilitating nonlinear interactions and synaptic depression, affect different STRF models, and if these effects can be captured with a context field (CF). Contextual effects were incorporated in simulated networks of spiking neurons, allowing one to define the true STRFs of the neurons. This, in turn, made it possible to evaluate the performance of each STRF model by comparing the estimations with the true STRFs. We found that currently used STRF models are particularly poor at estimating inhibitory regions. Specifically, contextual effects make estimated STRFs dependent on stimulus density in a contrasting fashion: inhibitory regions are underestimated at lower densities while artificial inhibitory regions emerge at higher densities. The CF was found to provide a solution to this dilemma, but only when it is used together with a generalized linear model. Our results therefore highlight the limitations of the traditional STRF approach and provide useful recipes for how different STRF models and stimuli can be used to arrive at reliable quantifications of neural computations in the presence of contextual effects. The results therefore push the purpose of STRF analysis from simply finding an optimal stimulus toward describing context-dependent computations of neurons along the auditory pathway.



from #Audiology via ola Kala on Inoreader http://ift.tt/2ay3vwF
via IFTTT

Capturing contextual effects in spectro-temporal receptive fields

Publication date: Available online 27 July 2016
Source:Hearing Research
Author(s): Johan Westö, Patrick J.C. May
Spectro-temporal receptive fields (STRFs) are thought to provide descriptive images of the computations performed by neurons along the auditory pathway. However, their validity can be questioned because they rely on a set of assumptions that are probably not fulfilled by real neurons exhibiting contextual effects, that is, nonlinear interactions in the time or frequency dimension that cannot be described with a linear filter. We used a novel approach to investigate how a variety of contextual effects, due to facilitating nonlinear interactions and synaptic depression, affect different STRF models, and if these effects can be captured with a context field (CF). Contextual effects were incorporated in simulated networks of spiking neurons, allowing one to define the true STRFs of the neurons. This, in turn, made it possible to evaluate the performance of each STRF model by comparing the estimations with the true STRFs. We found that currently used STRF models are particularly poor at estimating inhibitory regions. Specifically, contextual effects make estimated STRFs dependent on stimulus density in a contrasting fashion: inhibitory regions are underestimated at lower densities while artificial inhibitory regions emerge at higher densities. The CF was found to provide a solution to this dilemma, but only when it is used together with a generalized linear model. Our results therefore highlight the limitations of the traditional STRF approach and provide useful recipes for how different STRF models and stimuli can be used to arrive at reliable quantifications of neural computations in the presence of contextual effects. The results therefore push the purpose of STRF analysis from simply finding an optimal stimulus toward describing context-dependent computations of neurons along the auditory pathway.



from #Audiology via ola Kala on Inoreader http://ift.tt/2ay3vwF
via IFTTT

Capturing contextual effects in spectro-temporal receptive fields

Publication date: Available online 27 July 2016
Source:Hearing Research
Author(s): Johan Westö, Patrick J.C. May
Spectro-temporal receptive fields (STRFs) are thought to provide descriptive images of the computations performed by neurons along the auditory pathway. However, their validity can be questioned because they rely on a set of assumptions that are probably not fulfilled by real neurons exhibiting contextual effects, that is, nonlinear interactions in the time or frequency dimension that cannot be described with a linear filter. We used a novel approach to investigate how a variety of contextual effects, due to facilitating nonlinear interactions and synaptic depression, affect different STRF models, and if these effects can be captured with a context field (CF). Contextual effects were incorporated in simulated networks of spiking neurons, allowing one to define the true STRFs of the neurons. This, in turn, made it possible to evaluate the performance of each STRF model by comparing the estimations with the true STRFs. We found that currently used STRF models are particularly poor at estimating inhibitory regions. Specifically, contextual effects make estimated STRFs dependent on stimulus density in a contrasting fashion: inhibitory regions are underestimated at lower densities while artificial inhibitory regions emerge at higher densities. The CF was found to provide a solution to this dilemma, but only when it is used together with a generalized linear model. Our results therefore highlight the limitations of the traditional STRF approach and provide useful recipes for how different STRF models and stimuli can be used to arrive at reliable quantifications of neural computations in the presence of contextual effects. The results therefore push the purpose of STRF analysis from simply finding an optimal stimulus toward describing context-dependent computations of neurons along the auditory pathway.



from #Audiology via ola Kala on Inoreader http://ift.tt/2ay3vwF
via IFTTT