Electrochemical impedance spectroscopy of human cochleas for modeling cochlear implant electrical stimulus spread.

Cochlear implants (CIs) have tremendously helped people with severe to profound hearing loss to gain access to sound and oral-verbal communication. However, the electrical stimulus in the cochlea spreads easily and widely, since the perilymph and endolymph (i.e., intracochlear fluids) are essentially electrolytes, leading to an inability to focus stimulation to discrete portions of the auditory nerve, which blurs the neural signal. Here, we characterize the complex transimpedances of human cadaveric cochleas to investigate how electrical stimulus spread is distributed from 10 Hz to 100 kHz. By using electrochemical impedance spectroscopy (EIS), both the resistive and capacitive elements of human cochleas are measured and modeled with an electrical circuit model, identifying spread-induced and spread-independent impedance components. Based on this electrical circuit model, we implement a Laplace transform to simulate the theoretical shapes of the spread signals. The model is validated by experimentally applying the simulated stimulus as a real stimulus to the cochlea and measuring the shapes of the spread signals, with relative errors of <0.6% from the model. Based on this model, we show the relationship between stimulus pulse duration and electrical stimulus spread. This EIS technique to characterize the transimpedances of human cochleas provides a new way to predict the spread signal under an arbitrary electrical stimulus, thus providing preliminary guidance to the design of CI stimuli for different CI users and coding strategies.

Posttraumatic stress disorder in adopted children from Romania.

This follow-up study of 80 Romanian children showed that 16 (20%) of the children exhibited posttraumatic stress disorder (PTSD). The same children got scores in the clinical range on the Child Behavior Checklist (CBCL). These PTSD children could be differentiated from the remaining children by psychosocial but not by physical health variables. Children showing characteristics of PTSD stood out from the other subjects because of their scores on the Externalization dimension and excessive attention-seeking on the CBCL. The findings indicated that these Romanian adoptees exhibited survivor behavior. A substantial number of these adopted children require aftercare by adoption specialists from the time they arrive in Dutch families. It seems plausible that the high incidence of PTSD characteristics was related to extreme physical and social neglect occurring in the orphanages.

Trimorphism in foraminifera (protozoa) - verification of an old hypothesis.

The formation of megalospheric schizonts by a microspheric agamont has been observed for the first time in a foraminifer, the living nummulitid Heterostegina depressa. This finding verifies part of the hypothesis of biologic trimorphism and forces retraction of the recent hypothesis, that the schizont is a separate apogamic species and not part of a trimorphic cycle. The production of large numbers of schizonts can explain high schizont densities in natural populations.