Search

We introduce a one-dimensional spin injection structure comprising a ferromagnetic metal and a nondegenerate organic semiconductor to model electric current polarizations. With this model we analyse spin Coulomb dragging (SCD) effects on the polarization under various electric fields, interface and conductivity conditions. The results show that the SCD inhibits the current polarization. Thus the SCD inhibition should be well considered for accurate evaluation of current polarization in the design of organic spin devices.

The maturation of the auditory nerve's ability to encode temporal information in an acoustic signal was studied in young kittens, 7 to 23 days old, and in adult cats by measuring the degree to which auditory nerve fiber responses are synchronized (phase locked) to low frequency tones. The major findings include the following. In 7- to 10-day-old kittens thresholds are high (around 100 dB), and secure phase locking is observed only at frequencies below about 600 Hz. The upper frequency limit for phase locking in the adult, around 4 kHz, is reached gradually toward the end of the third postnatal week, a time when thresholds also reach their adult levels. The time course of development of the phase-locked response is similar for fibers with different characteristic frequencies (CFs). At all ages studied, the maximal phase synchrony at any given low frequency is generally obtained at stimulus intensities less than 20 dB above the rate threshold and some 10 to 30 dB below the saturation firing level of the fiber. Time delays, estimated from phase-versus-frequency plots, were similar across ages, although they tended to be longer and more variable at lower CFs during the first 2 postnatal weeks. Comparing the phase-locked response of auditory nerve fibers with that of the anteroventral cochlear nucleus neurons from a previous study suggested that the upper frequency limit for phase synchrony was reached later in the nucleus than in the nerve.

Tritiatedproline or horseradish peroxidase (HRP) was injected into the middle ectosylvian auditory cortex (AI) of one hemisphere in kittens during the first few weeks postpartum. Survival time was 24–96 hours. The tetra-methylbenzidine (TMB) (Mesulam '78) method was used to process the HRP material. By the first postnatal day (PND 1) most neurons retrogradely filled in the contralateral auditory cortex form a densely packed, continuous band that presumably represents mainly layer III. This continuous pattern is in contrast to that seen in the adult cat where callosal neurons tend to aggregate in clusters. Other retrogradely labelled cells are more sparsely distributed in deeper layers with the greatest accumulation being in layer VI. At this time callosal neurons are elongated, with their long axes parallel to radial cell columns. In autoradiographs on PND 2, silver grains are seen throughout the thickness of the cortex, indicating that callosal axons have reached the upper layers of the gray matter. Neither the alternating vertical columns nor the laminar bands of callosal afferents that characterize this projection in the adult are clearly seen in kittens of this age. By PND 8–12 the segregation of callosal afferents into vertical bands is evident in the gray matter; by PND 18 this pattern is well developed. On the other hand, the somata of callosal neurons of layer III retain their juvenile distribution well into the seventh postnatal week and show adultlike aggregations sometime around the 14th week after birth. Projections to the medial geniculate body, inferior colliculus, putamen, caudate nucleus, and pons are clearly evident early in the first postnatal week.

Microelectrode mapping and horseradish peroxidase oxidase histochemistry were combined to study the relationship between the characteristic-frequency representation and the intrinsic connectivity of the primary auditory cortex in the cat. Small extracellular iontophoretic injections of horseradish peroxidase within the characteristic-frequency map resulted in labeling of neuronal processes that, in the tangential plane, radiated out asymmetrically from the injection site over distances of several millimeters. The heaviest concentration of labeled fibers was along an axis parallel with the orientation of the isofrequency line within which the injection had been made. Thus, primary field neurons that have the same or a similar characteristic frequency have the potential of being preferentially interconnected.