Responses Of Single Nerve Fibers Research Articles

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.

Delay lines and amplitude selectivity are created in subthalamic auditory nuclei: the brachium of the inferior colliculus of the mustached bat.

1. The biosonar pulse of the mustached bat, Pteronotus parnellii parnellii, consists of four harmonics of a constant-frequency component (CF1-4) followed by a frequency-modulated component (FM1-4). FM-FM combination-sensitive neurons in the auditory cortex and the medical geniculate body (MGB) show facilitative responses to certain combinations of FM components in a pulse-echo pair. They are tuned to particular delays of echo FMn (EFMn) (n = 2, 3, or 4) from pulse FM1 (PFM1). The neural mechanisms for creating their response properties involve delay lines, coincidence detection, and multiplication. Coincidence detection and multiplication take place in the MGB. It is not yet known where and how delay lines are created. The first aim of the present studies is to examine whether delay lines are created by subthalamic nuclei. FM-FM neurons are tuned to not only echo delays but also echo amplitudes. Therefore, the second aim of the present studies is to examine the extent to which amplitude selectivity is created by subthalamic nuclei. Responses of single nerve fibers to acoustic stimuli were recorded from the brachium of the inferior colliculus (BIC) using tungsten wire microelectrodes, and their response latencies and best amplitudes were measured. 2. All BIC fibers responded strongly to single tone bursts. No FM-FM combination-sensitive neurons were found in the BIC. The best frequencies of BIC fibers were predominantly within the frequency ranges of four harmonics of the species-specific biosonar pulse. 3. The response latencies of BIC fibers tuned to FM1 were more diverse (3.5-15.0 ms) than those of BIC fibers tuned to FMn (3.8-6.5 ms). This difference in latency distribution was independent of stimulus amplitude. These data are consistent with the theory that delay lines utilized by FM-FM neurons are created by neurons tuned to the "FM1 frequency," and indicate that the delay lines are mostly, if not all, created in a subthalamic nucleus or nuclei. 4. The best amplitudes of BIC fibers tuned to FM1 or CF1 were 63.2 +/- 4.5 (SE) dB SPL, and those of BIC fibers tuned to FMn or CFn were 48.2 +/- 10.7 dB SPL. The distribution of the best amplitudes of BIC fibers were very similar to those of FM-FM and CF/CF neurons in the MGB. These data indicate that the amplitude selectivity of thalamic FM-FM and CF/CF neurons is mainly a product of a subthalamic nucleus or nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses of single nerve fibres to capsaicin applied to the skin

The responses of sensory nerve fibres to capsaicin solution topically applied to their cutaneous receptive fields were studied using the rat saphenous nerve. The polymodal nociceptors responded to capsaicin with discharge and subsequent densensitization to chemical, mechanical and thermal stimuli. Other types of C fibres, and Aβ and Aδ fibres, showed no response to capsaicin.

Development of the cat peripheral auditory system: input-output functions of cochlear potentials

Compound auditory nerve action potentials (APs) and cochlear microphonics (CMs) were recorded from the round-window of kittens aged 3–9 weeks and of adult cats. Animals were anaesthetized and pure tone stimuli were delivered via calibrated, sealed, transducer systems. AP and CM amplitude and AP latency were measured over a wide range of stimulus intensities (up to 80 dB SPL) and at 5 octave-interval stimulus frequencis (1–16 kHz). At low stimulus intensity levels, AP amplitude hadattained adult levels to low and high frequency stimuli by 6/12 weeks of age to mid-frequency stimuli by 9 weeks. As stimulus intensity levels were increased, the kitten input-output functions diverged progressively from those of the adults. At these higher intensity levels, AP amplitude maturation in even the 9 week animals was incomplete. AP latencies to stimuli of all frequencies shortened between the third and fourth weeks but remained stable thereafter. CM amplitude also reached maturity by the fourth week. These findings suggest that the development of AP after the fourth week consists of an increase in the synchrony of auditory nerve fibre responses, since both the fine structure of the cochlea and the responses of single nerve fibres are known to be mature by the end of the first postnatal month.

Tungsten ball microelectrode for extracellular single-unit recording

An electrolytic method is described for manufacturing ball-tipped tungsten microelectrodes. The tungsten ball is produced by slowly withdrawing the electrode from the etching solution until the wire mells and tungsten metal forms a ball at the end of the shaft. The size of the ball is related to both the size of the wire shaft and the amount of current being passed. Smaller balled tips are produced when wire of smaller shaft diameter is induced to spark and melt. Higher voltages and larger shaft diameters at sparking yield larger balled tips. Ball-tipped electrodes are produced easily and reliably by this method and require little training. Such electrodes are sturdy and capable of stably recording activity of either single cells or multiple-units with good signal-to-noise ratio. They can record extracellular perikaryal responses from neurons at several levels of the nervous system. Responses of single nerve fibers are not isolated by these electrodes.

Response of single nerve fibers at different hydrostatic pressures.

The effects of high hydrostatic pressure upon isolated single nerve fibers were investigated. Single nerve fibers were isolated from the nerve innervating the sartorius or semitendinosus muscle of the toad ( Bufo marinus). The responses of single nerve fibers were recorded using the ‘bridge-insulator,’ the ‘interface’ and the ‘three-compartment’ methods. Hydrostatic pressures up to 16,000 psi were developed with a hand operated hydraulic pump. The most striking effect of high pressures was the prolongation of the duration of the response. At 10,000 psi the duration was 4.5–5.0 times the duration at atmospheric pressures. The duration of prolonged responses (by previous tetanization) was not appreciably altered by high pressures. The amplitude, rheobase and shock-response interval were only slightly affected. At 5000 psi the shock-response interval increased by 5–15% and the rheobase by 10–15%.

Changes in the duration of the electric response of single nerve fibers following repetitive stimulation.

Single nerve fibers were isolated from the nerve innervating the sartorius or semitendinosus muscle of the toad (Bufo marinus). Single nerve fiber responses were recorded with three arrangements of the "bridge insulator" method. During stimulation at 50 to 150 pulses per second for 20 to 140 minutes the spike duration was progressively increased. After tetanization the spike duration usually continued to increase at a more rapid rate. Within 5 to 60 minutes further prolongation stopped and within 1 to 10 hours the spike duration was normal. The duration of the response of tetanized fibers was from 2.5 to more than 10 times the spike duration of untetanized fibers. Prolongation was observed in nerve fibers isolated from nerves tetanized in vivo.

The quantum character of light and its bearing upon threshold of vision, the differential sensitivity and visual acuity of the eye

A short introduction is given in § 1. In § 2 it is shown that one quantum of light absorbed by the photo-sensitive material in the eye suffices to give rise to the perception of light. In § 3 some relations are derived that are used in the discussions in § 4 and § 5. In § 4 and § 5 the attention is drawn to the statistical fluctuations in the numbers of quanta perceived and their relation to the limits of differential sensitivity and visual acuity of the eye. It is shown that the limits calculated in this way coincide surprisingly well with the limits actually observed. In § 6 some evidence is presented for the conception that the sensory cells (rods and cones) act in the same way as counters of light-quanta, the more complicated electrical response of single nerve fibers in the optic nerve being caused by the interaction of nerve-cells.