Measurement of stretch-evoked brainstem function using fMRI

Knowledge on the organization of motor function in the reticulospinal tract (RST) is limited by the lack of methods for measuring RST function in humans. Behavioral studies suggest the involvement of the RST in long latency responses (LLRs). LLRs, elicited by precisely controlled perturbations, can therefore act as a viable paradigm to measure motor-related RST activity using functional Magnetic Resonance Imaging (fMRI). Here we present StretchfMRI, a novel technique developed to study RST function associated with LLRs. StretchfMRI combines robotic perturbations with electromyography and fMRI to simultaneously quantify muscular and neural activity during stretch-evoked LLRs without loss of reliability. Using StretchfMRI, we established the muscle-specific organization of LLR activity in the brainstem. The observed organization is partially consistent with animal models, with activity primarily in the ipsilateral medulla for flexors and in the contralateral pons for extensors, but also includes other areas, such as the midbrain and bilateral pontomedullary contributions.

Efficacy of Computer-Based Noise Desensitization Training in Children With Speech-in-Noise Deficits

Purpose Auditory training is known to improve the speech-perception-in-noise (SPIN) skills in children with auditory processing disorders (APDs); however, conventional non–computer-based trainings are dreary and nonmotivating. This study intended to develop a computer-based noise desensitization training module in Indian English and test the efficacy of the same in children with APD having SPIN deficits. There are no such modules available at present to be used in Indian children. Method The module incorporated words-in-noise training, with monosyllables and trisyllables as target words in the presence of speech-shaped noise as well as multitalker babble at different signal-to-noise ratios ranging from +20 to −4 dB SNR. The study included 20 children with SPIN deficits diagnosed with APD and who were recruited randomly to the experimental group who received the training ( n = 10; M age = 11.1 years) and to the control group who did not receive any training ( n = 10; M age = 11.4 years). The outcome measures included behavioral measures and electrophysiological measures (auditory long latency responses for speech in quiet and noise). Results Compared to children in the control group, children in the experimental group exhibited improvements in the SPIN scores as well as temporal processing measures after training. Dichotic consonant–vowel tests and auditory memory and sequencing tests did not yield significant improvement post training. Also, auditory long latency responses in quiet and noise revealed significant reduction in the amplitudes after training. No significant difference was noted in the latencies of auditory long latency responses post training. Control group participants did not show any significant difference in any of the measures between the initial and follow-up evaluations. Conclusions The developed training module was successful in fetching improvements in behavioral and electrophysiological measures. It would be a great addition to the evidence-based rehabilitation support inventory for children with SPIN deficits in India. Supplemental Material https://doi.org/10.23641/asha.14551041

Effect of Hearing Aid Acclimatization on Speech-in-Noise Perception and Its Relationship With Changes in Auditory Long Latency Responses

Objective The study attempted to track speech-in-noise perception and auditory long latency responses (ALLRs) over a period of hearing aid use in naïve hearing aid users. The primary aim was to investigate the relationship of change in speech-in-noise perception with the change in ALLRs. Method Thirty adults with mild-to-moderate sensorineural hearing loss (clinical group) and 17 adults with normal hearing (control group) in the age range of 23–60 years participated in the study. Syllable identification in noise (SIN) and ALLRs in noise were measured three times (three sessions) over a period of 2 months of hearing aid use. Results Results showed a significant increase in SIN and a decrease in the latency of ALLRs in the later sessions compared to the baseline session in the clinical group. However, the changes seen across the three sessions in the control group were not statistically significant. The magnitude of change in ALLRs seen in the clinical group did not significantly correlate with the change in SIN scores seen in them. Conclusions The study provides evidence for improvements in speech perception in noise and in processing time of auditory cortical areas with hearing aid acclimatization. However, it is important to note that the improvement in ALLRs does not assure improvement in speech perception in noise.

Measurement of stretch-evoked brainstem function using fMRI

ABSTRACTKnowledge on the organization of motor function in the reticulospinal tract (RST) is limited by the lack of methods for measuring RST function in humans. Behavioral studies suggest the involvement of the RST in long latency responses (LLRs). LLRs, elicited by precisely controlled perturbations, can therefore act as a viable paradigm to measure motor-related RST activity using functional Magnetic Resonance Imaging (fMRI).Here we present StretchfMRI, a novel technique developed to study RST function associated with LLRs. StretchfMRI combines robotic perturbations with electromyography and fMRI to simultaneously quantify muscular and neural activity during stretch-evoked LLRs without loss of reliability. Using StretchfMRI, we established the muscle-specific organization of LLR activity in the brainstem. The observed organization is partially consistent with animal models, with activity primarily in the ipsilateral medulla for flexors and in the contralateral pons for extensors, but also include other areas, such as the midbrain and bilateral pontomedullary contributions.

StretchfMRI: a new technique to quantify the contribution of the reticular formation to long-latency responses via fMRI

Increased reticulospinal (RS) function has been observed to cause both positive and negative outcomes in the recovery of motor function after corticospinal lesions such as stroke. Current knowledge of RF function is limited by the lack of accurate, noninvasive methods for measuring RS function. Recent studies suggest that the RS tract may be involved in processing and generating Long Latency Responses (LLRs). LLRs, elicited by applying precisely controlled perturbations, can act as a reliable stimulus to measure LLR-related brainstem function using fMRI with high signal-to-noise ratio.In this paper, we present StretchfMRI, a new technique that enables simultaneous recording of neural and muscular activity during motor responses conditioned by velocity-controlled robotic perturbations, which allows for direct investigation of the neural correlates of LLRs using fMRI.Via preliminary validation experiments, we demonstrate that our technique can reliably elicit and identify LLRs in two wrist muscles–FCR and ECU. Moreover, via a single-subject pilot experiment, we show that the occurrence of an LLR in a flexor and extensor muscle modulates neural activity in distinct regions of the brainstem. The observed somatotopic organization is in agreement with the double reciprocal model of RS function observed in animal models, in which the right medullary and left pontine reticular formation are responsible for control of the motor activity in flexors and extensors, respectively.