Experimental Brain Research

Robertson, L.; Grimm, R.

doi: 10.1007/BF00234914pmid: 812716

221 23 23 5 5 L. T. Robertson R. J. Grimm Neurological Sciences Institute, Good Samaritan Hospital and Medical Center Portland Oregon USA Summary The activity of neurons in the dentate nucleus of the squirrel monkey was studied during the execution of a controlled, sequential movement that required different trajectories of the forelimb. Examination of 207 dentate neurons ipsilateral to the performing limb revealed that over 80% of the neurons isolated were distinctly correlated with performance. The majority of these neurons had a tonic discharge pattern that usually increased coincident with the start of the movement and was maintained throughout most of the performance. A smaller group of cells had a burst of activity that was restricted only to a narrow part of the performance. About 30% of the tonic neurons altered their pattern of discharge whenever different limb trajectories were required, but burst cells showed essentially no change. Detailed analysis of spike patterns revealed that no dentate neurons were phasically correlated with individual flexionextension cycles of the performance sequence. Dentate neurons appear to be related to some general function of motor performance rather than the actions of joints or muscles used to execute the task.

Sumner, B.

doi: 10.1007/BF00234915pmid: 1204692

221 23 23 5 5 B. E. H. Sumner Department of Physiology University Medical School Teviot Place Edinburgh Great Britain Summary The left hypoglossal nuclei of normal rats, and rats which had received left hypoglossal nerve axotomies 7–21 days previously, were studied by electron microscopy after injection of horseradish peroxidase as a marker of extracellular space and pinocytosis. Quantitative analysis showed that the number of pinocytotically-derived structures in presynaptic boutons was significantly increased in rats at 7, 14, and 21 days after axotomy when compared with normal rats. It was suggested that presynaptic boutons which became detached from injured neurones retracted by a membrane cycling mechanism involving pinocytotic uptake of bouton plasmalemma, without compensatory membrane production elsewhere. It was confirmed that the channels in the microglial cells communicated with the extracellular space.

Berthoz, A.; Pavard, B.; Young, L.

doi: 10.1007/BF00234916pmid: 1081949

221 23 23 5 5 A. Berthoz B. Pavard L. R. Young Laboratoire de Physiologie du Travail, CNRS-CNAM Paris France Dept. of Aeronautics and Astronautics MIT Cambridge Mass. USA Summary The basic characteristics of the sensation of linear horizontal motion have been studied. Objective linear motion was induced by means of a moving cart. Visually induced linear motion perception (linearvection) was obtained by projection of moving images at the periphery of the visual field. Image velocity and luminance thresholds for the appearance of linearvection have been measured and are in the range of those for image motion detection (without sensation of self motion) by the visual system. Latencies of onset are around 1 sec and short term adaptation has been shown. The dynamic range of the visual analyser as judged by frequency analysis is lower than for the vestibular analyser. Conflicting situations in which visual cues contradict vestibular and other proprioceptive cues show, in the case of linearvection a dominance of vision which supports the idea of an essential although not independent role of vision in self motion perception.

Beazley, L.

doi: 10.1007/BF00234917pmid: 1204693

221 23 23 5 5 L. D. Beazley Psychology Department University of Edinburgh Great Britain Summary In Amphibia all primary retinotectal nerve fibres cross at the chiasma. To investigate why this decussation takes place, a series of embryological operations were performed in which one host eye was replaced by an eye from the opposite side of a donor in Xenopus laevis. The visual projections to the optic tecta were mapped electrophysiologically in these animals when adult to reveal to which side of the brain the nerve fibres had become connected. In the majority of cases the contralaterally grafted eyes had developed primary projections to both tecta, in others all the fibres had innervated the contralateral tectum and in 2 animals optic axons were detected only from the ipsilateral side. In 2 other animals optic nerve fibres from both the normal and operated eyes had innervated both tecta. Control experiments showed that section of the optic nerve and stalk without any misalignment of the eye and stalk did not disturb the normal decussation of the fibres. Neither did enucleation in the embryo affect the decussation of the fibres from the remaining eye. It is concluded that no “side specificity” has been shown to exist to determine the side of the brain into which retinotectal fibres develop; rather it seems that complete decussation depends on the developing optic nerve fibres being able to enter a normally aligned optic stalk as they leave the eye.

Beazley, L.

doi: 10.1007/BF00234918pmid: 1204691

221 23 23 5 5 L. D. Beazley Psychology Department University of Edinburgh Great Britain Summary The development of intertectal neuronal connections has been investigated in Xenopus laevis. Contralateral eye grafts and enucleations were performed in embryos and the resultant visual projections to the optic tecta were mapped electrophysiologically after metamorphosis. In enucleated animals the ipsilateral projections were found to be normally organised retinotopically but consisted of visual units with abnormally large multi-unit receptive fields. In 10 animals with contralaterally grafted eyes a normal ipsilateral projection had developed from the abnormal eye and an abnormal projection from the normal eye, to produce congruent maps via the two eyes to one tectum. All the maps in these animals were retinotopically organised. In another 11 animals the ipsilateral projection from the operated eye was fragmentary or absent, while that from the unoperated eye resembled the pattern found after enucleation. Retinotopically abnormal contralateral projections had developed in 5 animals of this group. These results suggest that prefunctional specification determines the initial development of diffuse intertectal visual connections but these may be modified by a process of binocular interaction in the presence of a normal primary contralateral input.

Magnussen, S.; Glad, A.

doi: 10.1007/BF00234919pmid: 1204694

221 23 23 5 5 S. Magnussen A. Glad Institute of Psychology University of Oslo Norway Summary In psychophysical experiments the bright-dark contrast effects observed in a steady test-field were measured as a function of the temporal frequency of an inducing-field modulated symmetrically about the test-field luminance. The frequency-contrast functions obtained from these measurements were interpreted as reflecting the temporal frequency characteristics of the lateral pathways within the B and D systems (the on-center and off-center neurons) in human vision. Psychophysical evidence is further presented that the lateral neural pathways have lower temporal cut-off frequencies than the “straight-through” pathways. The results are discussed in terms of the frequency characteristics of the center and surround of the receptive fields of on-center and off-center neurons. It is doubtful, however, whether the psychophysical results can be fully explained by the properties of the single-unit receptive field mechanism.

Dichgans, J.; Wist, E.; Diener, H.; Brandt, Th.

doi: 10.1007/BF00234920pmid: 1204695

221 23 23 5 5 J. Dichgans E. Wist H. C. Diener Th. Brandt Neurologische Universitätsklinik mit Abteilung für Neurophysiologie Freiburg FRG Summary Apparent velocities of moving visual stimuli are known to be different depending on whether the subject pursues the stimulus (efferently controlled motion perception) or whether the eye is stationary and the image moves across the retina (afferent motion perception). Afferent motion perception of a periodic pattern or a moving single object causes overestimation of velocity (magnitude estimations) as compared to smooth pursuit. This socalled Aubert-Fleischl phenomenon is shown to depend on local temporal frequency stimulation on the retina caused by the repetitive passage of contrast borders of the moving periodic pattern. This is evidenced by the fact that for a given stimulus speed the amount of overestimation is a function of the spatial frequency of the pattern (or the angular subtend of a single moving object) and that the Aubert-Fleischl phenomenon is not observed if a single edge moves. Background characteristics seem not to influence the apparent velocity during smooth pursuit.

Paula-Barbosa, M.; Feyo, P.; Sousa-Pinto, A.

doi: 10.1007/BF00234921pmid: 1204696

221 23 23 5 5 M. M. Paula-Barbosa P. B. Feyo A. Sousa-Pinto Anatomical Institute Medical Faculty, University of Oporto Portugal Summary The association connexions of the peri-auditory (SF, Ea and INS) and auditory (AI, AII and Ep) areas of the cat cortex were studied in silver impregnated material of 32 experiments with cortical lesions. The cortex of the lateral bank of the rostral part of the middle suprasylvian sulcus (SF) sends many fibres to AI and to the insular cortex (INS), and has scanty projections upon AII and Ep. In addition, it sends fibres to the visual area 17 as well as to the ventral bank of the medial part of the cruciate sulcus. It receives fibres from the three auditory areas AI, AII and Ep, as well as from Ea and INS. The dorsal part of the anterior ectosylvian gyrus (Ea) projects upon SF, AI, and AII. Ea sends few fibres to Ep, and receives relatively dense projections from AI and AII. The anterior sylvian gyrus (INS) projects heavily upon AII as well as upon the superficial part of SF. It sends few fibres also to Ep. INS receives heavy projections from AII and relatively lighter connections from SF, AI and Ep. The three auditory areas AI, AII and Ep are strongly mutually interconnected. AI and Ep have scanty projections upon the visual area 19, and AI also to the lateral suprasylvian visual area, as well as upon the ventral bank of the medial cruciate sulcus. Correlations of the association connexions with the functions of each area are discussed.