Frequency selectivity in monkey auditory nerve studied with suprathreshold multicomponent stimuli

Data from non-human primates can help extend observations from non-primate species to humans. Here we report measurements on the auditory nerve of macaque monkeys in the context of a controversial topic important to human hearing. A range of techniques have been used to examine the claim, which is not generally accepted, that human frequency tuning is sharper than traditionally thought, and sharper than in commonly used animal models. Data from single auditory-nerve fibers occupy a pivotal position to examine this claim, but are not available for humans. A previous study reported sharper tuning in auditory-nerve fibers of macaque relative to the cat. A limitation of these and other single-fiber data is that frequency selectivity was measured with tonal threshold-tuning curves, which do not directly assess spectral filtering and whose shape is sharpened by cochlear nonlinearity. Our aim was to measure spectral filtering with wideband suprathreshold stimuli in the macaque auditory nerve. We obtained responses of single nerve fibers of anesthetized macaque monkeys and cats to a suprathreshold, wideband, multicomponent stimulus designed to allow characterization of spectral filtering at any cochlear locus. Quantitatively the differences between the two species are smaller than in previous studies, but consistent with these studies the filters obtained show a trend of sharper tuning in macaque, relative to the cat, for fibers in the basal half of the cochlea. We also examined differences in group delay measured on the phase data near the characteristic frequency versus in the low-frequency tail. The phase data are consistent with the interpretation of sharper frequency tuning in monkey in the basal half of the cochlea. We conclude that use of suprathreshold, wide-band stimuli supports the interpretation of sharper frequency selectivity in macaque nerve fibers relative to the cat, although the difference is less marked than apparent from the assessment with tonal threshold-based data.

Local field potentials in the BNST in patients with OCD: acute effects of DBS after symptom provocation

Introduction

Obsessive-compulsive disorder (OCD) is a disabling psychiatric disorder that affects 2-3% of the population. Pharmacological or cognitive behavioral therapy can reduce symptoms. Deep brain stimulation is emerging for treatment-resistant patients.

Objectives

We measured neuronal activity in two patients with treatment-resistant OCD, who had DBS electrodes implanted bilaterally in the BNST. Local field potentials were recorded directly from the BNST during and without symptom provocation and without electrical stimulation.

Methods

In two patients with a diagnosis of treatment resistant OCD (TR-OCD) local field potentials (LFP) were recorded as part of their clinical follow up post-implantation. In both patients, the diagnosis of TR-OCD was confirmed by a neuropsychiatric examination and a multidisciplinary committee comprising both experienced psychiatrists and neurosurgeons from different medical centers in Belgium. We used BrainSense recording technology in the Percept PC to record the LFPs. The LFP recordings in the first patient were acquired on the 15th day after DBS surgery. In the second patient, the interval between implantation and recording was 18 days. Symptom provocation was performed using the MOCCS image set, developed by Mataix-Cols.

Results

At rest, relative power peaks in the BNST were highest in the theta (4-8 Hz) frequency band for both patients. In both patients switching DBS ON during provocation images appears to cause the LFP signal to closely resemble that recorded during neutral images.

Conclusions

The main finding of this pilot study is that switching stimulation ON in the BNST during provocation images causes the LFP signal to more closely resemble the LFP recorded during neutral images.

Disclosure

No significant relationships.