Experimental Brain Research

Innocenti, G.; Manzoni, T.; Spidalieri, G.

doi: 10.1007/BF00236110pmid: 4853559

221 19 19 5 5 G. M. Innocenti T. Manzoni G. Spidalieri Institute of Human Physiology University of Catania Italy Institute of Human Physiology University of Ferrara Italy Istituto di Fisiologia Umana Università di Ferrara Ferrara Italy Summary 1. In the rostral part of the corpus callosum (somesthetic callosal region, SCR) fibres were identified, through which the callosally-projecting cells of the somatosensory areas transmit to the other hemisphere signals originated in the body surface. 2. With seriate macroelectrode penetrations it was found that, to some extent, the body surface is represented somatotopically in the rostrocaudal extent of the SCR. The strongest mass potentials to trigeminal, fore- and hindlimb stimulation were recorded from the rostral, middle and caudal portions of the SCR. The whisker region and the forelimb (both paws and proximal segments) appeared to have the widest callosal representation. 3. Ablation experiments showed that callosal somesthetic fibres originate in both SI and SII areas and that only impulses set up in the contralateral hemibody are relayed in these areas. Direct stimulation of the latter evoked within the SCR mass potentials whose rostrocaudal distribution parallels that of the peripherally evoked responses. 4. Exploring the SCR with microelectrodes, 43 spontaneously active fibres were isolated, all reactive to electrical and physiological stimulation of the related peripheral receptive fields. These were located in trigeminal (31 fibres), segmental (10 fibres) or both in trigeminal and segmental regions (2 fibres). The extent of the receptive fields and the reactivity characteristics of almost all the fibres sampled were lemniscal in type, and similar to those of the somatotopic neurones of cortical somatosensory areas.

Straschill, Max; Schick, Frede

doi: 10.1007/BF00236111pmid: 4853329

221 19 19 5 5 Max Straschill Frede Schick Max Planck Institut für Psychiatrie München FRG Summary 270 single neurons from the anterior part of the middle suprasylvian gyrus (AMSS) were recorded in awake and non-paralyzed cats (Chronic preparation). 10% were unresponsive to visual stimulation, the remainder reacted well to moving visual stimuli . Half of the units tested were directionally selective. Horizontal, or downward preferred directions predominated. Most neurons were relative insensitive to changes of shape, orientation, contrast, and velocity of the visual stimulus. Some neurons preferred rapid (100°/sec) jerky movements, others required complex motions of irregular shapes, a few strongly preferred objects moving towards the animal in the midsagittal plane. 40% of neurons yielded phasic On-Off reaction to flashing stationary spots. Habituation to repeated stimulation was a common feature and occured in 50% of AMSS neurons. In 19% of neurons tested the discharge rate was not affected by saccadic eye movements, when the animal faced a patterned background. Among the remainder two types of saccade associated responses could be distinguished. Type I discharged prior to or simultaneously with the onset of saccades. This early response was usually associated with saccades of particular directions. Saccades in total darkness yielded weaker and less consistent responses. Type II discharged subsequent to the onset of the saccades after a latency of 40 msec (type IIa), 40–80 msec (type IIb) and 80 msec (type IIc). Responses of type IIa are probably consequences of the retinal effects of eye movements. The saccade associated responses of type Ia, IIb and IIc are tentatively interpreted as results of an eye movement-synchroneous subcortical input, which facilitates transmission in AMSS neurons. Presaccadic facilitation, which generates type Ia responses, may be functionally related to shifts of attention prior to eye movements. It is suggested that postsaccadic facilitation, which underlies the reactions of type IIb and IIc, may be a correlate of visual attention during the fixation period.

Klee, M.; Pierau, F.; Faber, D.

doi: 10.1007/BF00236112pmid: 4854613

221 19 19 5 5 M. R. Klee F. -K. Pierau D. S. Faber W. G. Kerckhoff-Inst., Max-Planck-Gesellsch. Bad Nauheim FRG Max-Planck-Inst. für Hirnforschung, Neurobiolog. Abt. Frankfurt/M-Niederrad FRG Dept. Physiol. Univ. Cincinnati Cincinnati Ohio USA Summary During intracellular recording from cat spinal motoneurons, the lumbo-sacral cord was subjected to rapid local temperature changes. Cooling to 30° C causes a decrease in the resting membrane potential (RMP), a transient increase in spike overshoot, and increases in the input resistance and the durations of both the action potential and the hyperpolarizing after-potential (HAP). Warming causes these membrane parameters to change in the opposite direction and can result in a failure of antidromic activation. The RMP changes are dependent upon the RMP at normal temperature, being negligible in cells having an initial RMP greater than 70 mV. The Q 10 -values of the three peaks of the differentiated spike are relatively high and nearly identical to the Q 10 -values of the corresponding rate constants for sodium activation and inactivation and potassium activation measured by Frankenhaeuser and Moore in toad nerve fibers, i.e. 1.71, 2.35 and 3.12, respectively. Delayed sodium inactivation and potassium activation explain the increase in spike overshoot observed during cooling, and the high Q 10 of potassium activation is nearly identical to the Q 10 of the time to peak of the HAP (3.12 vs. 2.97). The decrease in RMP during cooling is attributed to a decrease in the P K ∶P Na ratio rather than to a blockage of an electrogenic sodium pump; the differences in RMP temperature sensitivities between cells with high and low initial RMP's might be due to a higher resting P K (anomalous rectification) at higher RMP. We conclude that the electrogenic pump does not normally contribute significantly to the RMP of cat motoneurons.

Phillips, W.; Singer, W.

doi: 10.1007/BF00236113pmid: 4852102

221 19 19 5 5 W. A. Phillips W. Singer Psychology Department Stirling University Scotland Max-Plank-Institute for Psychiatry Munich FRG Summary Psychophysical experiments were conducted to determine the conditions under which human observers can detect small differences between two successively presented random-dot patterns. The inter-stimulus interval (ISI) varied from 20 to 500 msec. It was found that the appearance of an additional light spot in the second pattern was detectable with ISIs of up to 120 msec. The disappearance of a light spot from the first pattern was detectable with ISIs up to 60 msec. Decreasing the exposure duration of the first pattern worsened the detection of appearance but improved the detection of disappearance. In contrast, decreasing the exposure duration of the second pattern improved the detection of appearance but worsened the detection of disappearance. If the first pattern was presented to one eye and the second pattern to the other under conditions of binocular fusion neither appearance nor disappearance could be detected at any ISI. The results are interpreted as evidence that the transient neural response to the onset of a stimulus is significantly affected by the offset of that stimulus within the preceding 120 msec, and that the transient neural response to the offset of a stimulus is significantly affected by the onset of that stimulus within the following 60 msec. It is suggested that reciprocal inhibition between on- and off-activity could account for these results.

Singer, W.; Phillips, W.

doi: 10.1007/BF00236114pmid: 4368733

221 19 19 5 5 W. Singer W. A. Phillips Max-Planck-Institute for Psychiatry Munich FRG Psychology Department Stirling University Scotland Summary Neuronal responses to interruptions of light stimuli were studied in 58 X-type and 7 Y-type LGN relay cells with intra- and extracellular recording techniques. The responses to interruption were then compared with responses to either appearing or disappearing light stimuli which had the same luminance and size as the interrupted stimulus. The extent to which responses to interruption differed from those to appearance and disappearance was studied as a function of the interstimulus interval (ISI), the duration of the stimulus before the interruption (t 1 ) and after the interruption (t 2 ). Responses to stimuli appearing after interruptions of up to 500 msec were weaker than those to appearance and disappearance. This difference decreased with increasing ISI. The difference between responses to appearance and interruption increased as t 2 decreased, and decreased as t 1 decreased. The reverse was true for the difference between responses to disappearance and interruption. Stimulation of the mesencephalic reticular formation consistently reduced the difference between responses to appearance and disappearance compared with those to interruption for all stimulus conditions. These results are discussed in the context of the psychophysical study presented in the preceding paper. It is shown that the neuronal reactions are reflected in detail by the ability of humans to detect appearances and disappearances that occur during interruptions. EPSP sequences recorded from LGN relay cells and relay cell responses conditioned by reticular stimulation suggest that the differentiation of responses to interruption and change partially occurs already in the retina. This differentiation is subsequently enhanced by antagonistic inhibition in the LGN. It is proposed that these inhibitory interactions at peripheral sites of the visual pathway store visual information and serve to reduce the redundancy of responses to short interruptions of the visual input. Centrifugal modulation of LGN inhibition is proposed to control the trade off between temporal integration and temporal resolution.

Duggan, A.

doi: 10.1007/BF00236115pmid: 4854720

221 19 19 5 5 A. W. Duggan Department of Pharmacology Australian National University Canberra Australia Summary Spinal interneurones activated with a short latency from peripheral nerves were more sensitive to L-glutamate than to L-aspartate. Renshaw cells were more sensitive to L-aspartate than to L-glutamate. These findings are consistent with the hypothesis that L-glutamate is the transmitter released by primary afferent fibres and L-aspartate is that released by spinal excitatory interneurones.

Knyihár, Elizabeth; László, I.; Tornyos, S.

doi: 10.1007/BF00236116pmid: 4852049

221 19 19 5 5 Elizabeth Knyihár I. László S. Tornyos Department of Anatomy University Medical School Szeged Hungary Summary Fluoride resistant acid phosphatase (FRAP) activity of the rat substantia gelatinosa Rolandi is confined to electron dense sinusoid terminals under normal conditions. Transection of dorsal roots or removal of dorsal root ganglia results in a rapid degeneration of more than half of the electron dense sinusoid axon terminals. First signs of degeneration ensue 20 hours after surgery; at the 24 hours state osmiophilic degeneration bodies develop that are translocated into glial elements in the course of the second postoperative day. At the same time, light microscopically visible FRAP-activity of the Rolando substance disappears. Electron histochemical investigations reveal that decreased enzyme activity is due to degeneration of FRAP-positive terminals. It is concluded that FRAP-positive terminals, representing the majority of electron dense sinusoids in the Rolando substance, are dorsal root collaterals; the origin of non-degenerating FRAP-negative electron dense terminals remains unknown for the time being.