Radiative reactions in two and three nucleon systems

Summary We have reviewed the theoretical and experimental situation regarding radiative processes in two and three nucleon system. There has actually been a lot of recent progress. Data sets from different experiments which agree with one another have now replaced the factor of two discrepancies of just a few years ago for several of the processes. New data on spin observables are now available for a variety of energies. New experiments are in progress for both proton proton and neutron bremsstrahlung. The theorists have not kept up. Although there has been a lot of work, there exists no theory which quantiatively describes all the data for eithern + p d + or forp + d ³He + . Thus there is still a lot to do if we are to fully understand these most basic processes.Invited talk to the symposium Measons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.Support in part from the Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged.     

Asymmetrical hippocampal connectivity in mesial temporal lobe epilepsy: evidence from resting state fMRI

Background

Recent studies have shown that the human right-hemispheric auditory cortex is particularly sensitive to reduction in sound quality, with an increase in distortion resulting in an amplification of the auditory N1m response measured in the magnetoencephalography (MEG). Here, we examined whether this sensitivity is specific to the processing of acoustic properties of speech or whether it can be observed also in the processing of sounds with a simple spectral structure. We degraded speech stimuli (vowel /a/), complex non-speech stimuli (a composite of five sinusoidals), and sinusoidal tones by decreasing the amplitude resolution of the signal waveform. The amplitude resolution was impoverished by reducing the number of bits to represent the signal samples. Auditory evoked magnetic fields (AEFs) were measured in the left and right hemisphere of sixteen healthy subjects.

Results

We found that the AEF amplitudes increased significantly with stimulus distortion for all stimulus types, which indicates that the right-hemispheric N1m sensitivity is not related exclusively to degradation of acoustic properties of speech. In addition, the P1m and P2m responses were amplified with increasing distortion similarly in both hemispheres. The AEF latencies were not systematically affected by the distortion.

Conclusions

We propose that the increased activity of AEFs reflects cortical processing of acoustic properties common to both speech and non-speech stimuli. More specifically, the enhancement is most likely caused by spectral changes brought about by the decrease of amplitude resolution, in particular the introduction of periodic, signal-dependent distortion to the original sound. Converging evidence suggests that the observed AEF amplification could reflect cortical sensitivity to periodic sounds.