Isolated and identified crab axons have been used to study the forms of the repetitive responses to direct current. Using techniques which enable the responses of isolated axons to be studied at the site of imposed electrical currents, the responses can be classified into five major groups with two subdivisions:- Group 1. Axons showing no marked supernormality during the recovery cycle, that repeat over a wide range of frequencies when stimulated by direct current, with frequency increasing smoothly with the strength of applied current, Group ia. To direct current these axons yield a train of impulses, the intervals between which progressively lengthen. Group ib. To direct current these axons yield a train of impulses the Intervals between which, for some time at least, progressively shorten. Group ll. Axons showing a pronounced supemomality during the recovery cycle, that repeat over only a limited frequency range. Group lla. Axons capable of long latencies, with oscillatory subthreshold potentials before and after the repetitive response. Group llb. Axons showing only short latencies, and lacking subthreshold oscillations before the repetitive response, but nevertheless with oscillations following the response. Group lll. Axons with a prolonged long-lived supemormality during the recovery cycle, which can be correlated with a prolonged action potential. They can repeat over a wide range of frequencies stimulated by direct current, but lack true local potentials for all action potentials except the first. Group lV. Axons with a relatively prolonged subnormality during the recovery cycle. They show short trains of action potentials, the amplitude of which progressively decreases even to near threshold currents, and the interspike intervals show a smooth increase. Group V. Axons unable to repeat to direct current, having a low safety factor and high threshold. They are capable of only short latencies. The single action potential shows a considerable variation in amplitude. A wide varied of experiments have been carried out, which have shown that several factors influence the form of the repetitive response in crab axons, and that the inadequacy of previous theories stems from their oversimplification. The factors show to operate in determining the form of these responses are:- 1. Changes in the resistance of the axon membrane, so that a constant current pulse will not cause the sane potential displacement while it acts. These changes can occur as the result of ionic accumulation outside the axon, or from the active process of delayed rectification. 2. The duration and from of the recovery cycle limits the upper frequency of the repetitive response, as well as influencing it at other times. 3. Sustained depolarisation depresses excitability, by lengthening the repolarisation time of an action potential and the period of recovery following it, as can be seen when the threshold potential for the spike rises throughout a repetitive response. 4. Changes in the membrane potential that result from the accumulation of ions in the near vicinity of the axon membrane. These changes, although they show some interdependence, are often difficult to completely eliminate any particular one by experiment. Although these factors have not been measured quantitatively, on account of technical difficulties inherent in the use of crab axons, they are sufficient to provide a coherent interpretation of repetition.

1. Peripheral nerve from the crab walking leg was seen to take up nicotinic acid (NA) to an extent ten times greater than the surrounding tissues (p.37). 2. After a labelled dose of NA there was a gradient of radioactivity in the nerve trunk with the maximum peripherally (p.40). 3. Individual fibres from the trunk were seen to take the *NA up in equal amounts, irrespective of their function (p.47). 4. No such gradient was seen in a length of nerve immersed in a bath containing *NA (p.45). 5. A substance was extracted from the nerve after injection of the *NA which was radioactive (p.49), and which was seen to have reactions of a small peptide (p.57). 6. This substance was also seen to have an accelerating effect on the crab heart, but had no detected effect on the contractions of the closer muscle in the leg (p.68). 7. In the second part of the thesis, results show that there is no difference in the structure of the sheath around the different motor axons in the crab leg, as seen under the light microscope (p.108). 8. When the potassium concentration around an isolated axon was changed to three times its normal value, the resulting drop in the membrane potential and resistance was slower and smaller than for any other concentration tried (p.113). 9. The effect of applying to single fibres dinitrophenol and other compounds of pharmacological interest was studied; with the dinitrophenol the membrane resistance was seen to fall reversibly in the manner described for other preparations (p.120).

Present knowledge indicates the importance of one region of monkey temporal association cortex, the superior temporal sulcus (STS), in predominantly high level analysis of 'biologically' important objects. To clarify and elaborate on the function of the monkey STS, the following questions are addressed: (1) what kind of tactile processing occurs in the polymodal STS and does it compare with the complex visual processing observed; (2) does behavioural sensitivity to face and body information parallel neural sensitivity (of STS cells) to the same stimulus dimensions; (3) does monkey STS ablation result in a behavioural indication of impairments in the perception of socially relevant stimuli; and (4) are visual cells in the STS sensitive to social communicational elements of facial or postural expression? Single-unit recording studies of the macaque STS (using standard techniques in awake, behaving animals) reveal a population of somatosensory neurones, with large receptive fields, sensitive only to unexpected (unpredictable) tactile stimulation. Complex tactual-visual interactions observed stress the importance of this dimension of processing. A separate population of visual cells exhibit sensitivity to compound facial expressions and head/body postures important in primate social communication. A behavioural study of monkeys' socio-emotional responses to configurational aspects of faces, the posture of the head and the interaction of form and motion, reveal their ability to discriminate salient cues in the context of social communication/interaction. It is tentatively shown that monkeys with the STS ablated are unable to make such discriminations, so reacting inappropriately to the stimuli (a symptom of Kluver-Bucy syndrome). The combined findings show that the STS performs a multimodal perceptual analysis of socially relevant stimuli, and suggest that the STS provides a sensory input to a limbic structure, such as the amygdala, through which it mediates appropriate emotional reactive behaviour.

by Communications Biophysics Group of Research Laboratory of Electronics and William M. Siebert. / "July 7, 1959"--Cover. / Includes bibliographies. / Army Signal Corps Contract DA36-039-sc-78108. Dept. of the Army Task 3-99-06-108 and Project 3-99-00-100.