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H Silfvenius

Publications and source records attributed to H Silfvenius.

At least 55 records · Page 3Linked to original sources
PubMed1984

Preoperative and postoperative memory testing of epileptic patients.

The present paper has four main objectives. First, it proposes a general theoretical orientation of memory functions as a basis for the research to be discussed. This framework is functionalistic/interactionistic in nature, in that memory is seen as an interaction between available cognitive capabilities of the individual and specific demands of the situation in which the individual is to remember a certain set of materials. Secondly, on the basis of this framework certain methodological requirements are discussed. These considerations take into account the need for a proper analysis of the to-be-remembered (TBR) information and those cognitive functions involved in remembering the TBR information presented. Thirdly, a preoperative and postoperative memory test is presented. This was designed on the basis of the theoretical and methodological considerations mentioned. Data from one such ongoing study is presented, taking into account various measures of memory functions; immediate free recall, final free recall, final cued recall, serial recall, final final free recall, short-term memory and long-term memory capacity as measured by the Tulving & Colotla [1] lag measure, primacy, asymptote and recency effects, and semantic memory. Finally, on the basis of the experience from this memory test a few aspects of memory testing in epileptic patients are suggested for future research.

Adolescent↗
PubMed1980

Topical application of penicillin into hippocampal in vitro slices: A methodological study using benzyl (14C) penicillin.

A gas pressure system is employed for topical application of pico/nanolitre volumes of 9 mmol/l benzyl (14C) penicillin into guinea-pig in vitro transverse hippocampal slices. Control of pressure pulse parameters enables ejectates, computed after liquid scintillation, from 10 micrometer, 5 micrometer and 2 micrometer pipettes with high reliability of ejection. A detailed study was done on the ejection performance of 5 micrometer and 2 micrometer pipettes. It shows that for the 5 micrometer tips, with the chosen ejection parameters, feeding pressure = 0.5 MPa, feeding pulse duration 50 ms, a 99% ejection incidence was obtained (n = 200). The mean volumes ejected were 0.12 and 0.5 nl (n = 50) for one and four pulses delivered respectively. The corresponding ejectate means obtained from five 2 micrometer pipettes given a feeding pressure of 1.5 MPa, and a feeding pulse duration of 70 ms, were 0.04 and 0.13 nl. Statistical evaluation of the individual pipette ejection performances gave characteristic regression slopes within each pipette group. A comparison between visually controlled injection into oil and injection into slice, showed a close correspondence. The applicability of the ejection method is discussed in relation to functional studies on the conversion of single neurones into "epileptic" ones.

Administration, Topical↗
PubMed1980

A comparison of distal and proximal dendritic synapses on CAi pyramids in guinea-pig hippocampal slices in vitro.

1. In vitro slices of guinea-pig hippocampus have been employed to compare excitatory synapses located distally and proximally on the dendritic tree of CA1 pyramidal cells.2. The main orientation of unmyelinated afferent fibres was found to be parallel to each other and perpendicular to the dendritic axis.3. The density of boutons ending on dendritic spines was roughly similar throughout the greater part of the dendritic tree with an average of 42 +/- 7.2 synapses per 100 mum(2). Their number did, however, decrease in the distal fifth of the apical and in the distal third of the basal dendritic region in parallel with an increase of boutons on the dendritic shafts.4. Negative synaptic field potentials (extracellular field e.p.s.p.s) had their maximum in the region where activated afferent fibres terminated and showed reversal when recorded from sufficiently displaced positions along the dendritic axis. The field e.p.s.p. was preceded by a diphasic presynaptic fibre volley. By cutting all but a narrow bundle of afferent fibres selective activation of a small group of dendritic synapses was possible. Stimulation of fibres crossing tissue bridges (35-100 mum wide) evoked field e.p.s.p.s comparable in amplitude to those seen in slices without lesions. The size of the field e.p.s.p.s evoked via distal and proximal bridges was remarkably similar and linearly related to the size of the appropriate stimulus current and presynaptic volley.5. Selective activation of a small group of afferent fibres gave rise to large amplitude population spikes. Proximal and distal bridges were largely equipotent when they were equally wide. Above the threshold amplitude, the evoked population spikes were linearly related to both the presynaptic volley and the stimulus current. Constant current stimulation of fibres at all apical dendritic levels was equally effective in evoking population spikes, with the exception of the outer fifth of the tree where stimulation was unsuccessful. Input across distal or proximal bridges (400 or 50 mum from the soma) also gave the same high probability of discharge of single units (1.0 for thirty-five of thirty-six cells).6. An input across a narrow and distal bridge (35 mum), representing less than 5% of the fibres synapsing on the apical dendrite, was sufficient to give a firing probability of 1.0 for all cells tested (fifteen).7. For seventeen cells pairs of equally wide distal and proximal apical dendritic bridges were compared. Both inputs gave a mean probability of firing above 0.95 with stimulation strengths less than 2.5 times the spike threshold.8. Intracellular e.p.s.p.s had similar shapes following activation across distal and proximal dendritic bridges. The amplitude of neither type was significantly affected by hyperpolarization of the soma up to 25 mV. The half-width was prolonged to the same moderate degree for both inputs.9. The firing level for the action potential was similar for proximal and distal dendritic inputs and for spikes excited by depolarizing current pulses across the soma membrane.10. The apparent equipotentiality of synchronously activated distal and proximal dendritic synapses is discussed in the light of the known histology of the CA1 pyramidal cells.

Action Potentials↗
PubMed1978

Functional characteristics of unmyelinated fibres in the hippocampal cortex.

(1) In transverse hippocampal slices (350 micrometer thick), taken from guinea pigs initially anaesthetized with ether, intracortical afferent fibres were activated by small current pulses delivered through tungsten microelectrodes. Extracellular potentials were recorded from the zone of activated fibres in dendritic layers while intracellular recordings were made from the soma of CA1 pyramidal cells. (2) When recording was made from the same level as the stimulating cathode, the extracellular potential consisted of a diphasic deflection followed by a larger negative wave with a superimposed population spike. The negative wave corresponded to an intracellularly recorded EPSP, and is called an extracellular EPSP, whereas the initial diphasic deflection had no intracellular counterpart. (3) The initial diphasic deflection was linearly related to the size of both the intracellular and extracellular EPSP. It was not changed by removal of calcium ions from the bathing fluid, whereas all postsynaptic activity disappeared. The diphasic deflection was propagated along fibres lying parallel to the pyramidal layer with a velocity of 0.3 m/sec. It could follow short bursts of stimulation at 300 Hz. The absolute refractory period was 2.0 msec. (4) The initial diphasic deflection is interpreted as the compound action potential of the largely unmyelinated afferent fibres to the CA1 neurones.

Afferent Pathways↗
PubMed1977

Axon-collateral activation by dorsal spinocerebellar tract fibres of group I relay cells of nucleus Z in the cat medulla oblongata.

1. The problem whether the group I hind limb cerebral tract and the dorsal spinocerebellar tract (DSCT) have common spinal axons has been investigated in the present study. 2. Thirty-two cells located in the nucleus Z of the cat medulla oblongata and activated by spinal fibres in the dorsolateral fascicle were selected for the study. 3. Extracellular recording from these neurones demonstrated that most of them were monosynaptically linked to spinal fibres excited by ipsilateral hind limb group I muscle afferents. The cells exhibited a restricted spatial convergence and had a limited excitatory convergence from group II muscle and from skin afferents. 4. Antidromic activation from the contralateral thalamus showed that they were bulbothalamic relay cells. 5. Cerebellar surface or depth stimulation activated 88% of the twenty-six cells tested at a short latency. With a collision technique it was demonstrated that twelve out of twenty-three (52%) of these group I relay neurones were activated by axon-collaterals of the DSCT. 6. 43% of the cells activated from the cerebellum, but not proven to be linked to the DSCT, could, nevertheless, have been excited by DSCT axon-collaterals, if it is assumed that different fibres converging with excitation on the group I relay cells were activated in the collision test.

Afferent Pathways↗
PubMed1977

Input from ipsilateral proprio- and exteroceptive hind limb afferents to nucleus Z of the cat medulla oblongata.

1. Extracellular recordings have been made from proprio- and exteroceptive neurones in nucleus Z of the cat medulla oblongata. 2. Seventeen non-relay cells were excited by ipsilateral hind limb group I muscle afferents. Their functional were similar to those of the corresponding relay cells (Johansson & Silfvenius, 1977), i.e. activation by axon-collaterals of dorsolateral fascicle (DLF) fibres was observed, indicative of an input from the dorsal spinocerebellar tract (DSCT) to these neurones. The non-relay cells differed, however, from the relay cells in that a larger proportion of them were disynaptically connected to the spinal fibres. It is suggested that the non-relay cells by inhibition modulate the group I relay transmission in nucleus Z. 3. Fifteen cells were excited by ipsilateral hind limb low threshold skin afferents with their spinal fibres at the first cervical segment located either in the DLF or in the dorsal column (DC). Evidence for a cutaneous hind limb bulbothalamic path independent of that of the DC and of the spinocervicolemniscal path is presented. 4. Six cells were activated by ipsilateral hind limb joint afferents at low threshold. At the C1 level the spinal fibres were located either in the DLF or in the DC. No joint activated relay-cells were encountered. Axon-collateral activation of DLF-linked joint cells was observed during cerebellar stimulation, indicating that segmental DSCT cells mediated the joint input to nucleus Z. 5. The topographical organization within nucleus Z and its input relation to the DSCT is discussed.

Afferent Pathways↗
PubMed1977

Connexions from large, ipsilateral hind limb muscle and skin afferents to the rostral main cuneate nucleus and to the nucleus X region in the cat.

1. Evidence is presented for an input from ipsilateral hind limb group I muscle afferents and low threshold cutaneous afferents, to cells in the rostral division of the main cuneate nucleus (rMCN) and in the region of the descending vestibular nucleus and the nucleus X of Brodal & Pompeiano (1957a), the (DV-X). 2. Thirteen group I-rMCN cells were recorded from. The functional properties of these cells were similar to those of nueleus Z (Landgren & Silfvenius, 1971; Johansson & Silfvenius, 1977a, b). The cells were monosynaptically linked to spinal dorsolateral fascicle (DLF) fibres. Nine cells projected to the contralateral thalamus, i.e. a second group I hind limb bulbothalamic tract is described. Ten cells were synaptically activated from the ipsilateral cerebellum from the anterior projection zone of the dorsal spinocerebellar tract (DSCT). Axon-collateral activation by DSCT fibres was established for two of these cells. They were both bulbothalamic relay cells. For the remaining eight cells, activated from the cerebellum, this was not proven. These cells could, however, either be linked to DSCT fibres or to short axon-collaterals of a cell body of unknown location. A projection from the rMCN to the cerebellum is described and agrees with recent anatomical findings. Two cells were not excited from the cerebellum. 3. Four rMCN cells were activated by cutaneous afferents with their secondary axons in the DLF. Suggestive evidence for a bulbothalamic cutaneous hind limb path via the rMCN is presented. Two cells were activated from the cerebellum, presumably via axon-collaterals of nonsegmental cells. 4. Eight group I-DV-X cells were recorded from. They were monosynaptically linked to spinal DLF fibres and resembled functionally the nucleus Z and rMCN cells when stimulated from the periphery. Two cells projected to the contralateral thalamus, and two others were synaptically excited. Seven cells were activated from the ipsilateral cerebellum. Two of them projected to the cerebellum, and three were synapitcally activated by axon-collaterals of an undefined non-segmental cell. 5. Two DV-X cells which were activated by cutaneous afferents possibly had their spinal fibres deep in the dorsal column. Both were activated from the cerebellum, one by collaterals of a spinal axon. The functional organization of the three juxtaposed medullary nuclei, Z, rMCN and DV-X is discussed.

Afferent Pathways↗
PubMed1975

Columnar distribution of U-fibres from the postcruciate cerebral projection area of the cat's group I muscle afferents.

Needle stitch lesions were made in the maximal point of the cerebral projection area of the low threshold muscle afferents near the postcruciate dimple of the cat's posterior sigmoid gyrus. The lesions did not exceed 500 mum in diameter and were restricted to the cortical grey matter. Degenerating nerve fibres and terminals were investigated with Fink-Heimer technique in four cats (survival times: 26, 48 and 96 hours). The cytoarchitectonic areas of the sensori-motor cortex were determined in cresyl violet and van Gieson sections. All lesions were made in area 3a. Degenerating U-fibres originating from the lesion travelled in the white matter to the cortex of area 4 gamma, 3b and 2. They reentered the cortex and branched in layer III. Terminal degeneration was found in layer I. The degeneration was distributed to distinct columns with a diameter of about 1mm. Such columns were observed laterally and medially in area 4 gamma, in area 3b near the caudal end of the coronal sulcus, in area 2 near the lateral ansate sulcus and in the forelimb region of SII. The distribution of the cortico-cortical connections from the cerebral projection area of the forelimb group I muscle afferents was discussed in relation to the known cerebral projections of group I muscle afferents, low threshold joint afferents, pacinian afferents and low threshold skin afferents.

Animals↗
PubMed1971

Nucleus Z, the medullary relay in the projection path to the cerebral cortex of group I muscle afferents from the cat's hind limb.

1. The medullary relay of hind limb muscle afferents was studied in cats anaesthetized with chloralose. Evoked potentials were recorded from the dorsal surface of the medulla oblongata and from the depth of the medulla with penetrating micro-electrodes. Graded electrical stimulation of the muscle nerves was used. The afferent volley was monitored by recordings from the lumbar dorsal roots or from the peripheral nerves.2. Group I muscle afferents from the ipsilateral quadriceps, posterior biceps-semitendinosus and gastrocnemius-soleus nerves evoked potentials in the nucleus Z of Brodal & Pompeiano (1957a). Focal and unitary potentials were recorded within 2.7-3.8 mm rostral to the obex and 2.8-4.1 mm lateral to the mid line. The recording positions were checked histologically.3. Focal and unitary responses appeared at threshold strengths of the afferent volleys. The latencies of the focal potentials varied between 4.5 and 7.0 msec, those of the unitary ones between 5.1 and 11.0 msec. Group II muscle afferents and low threshold cutaneous afferents also projected to nucleus Z.4. An antidromic discharge was evoked in the relay cells of nucleus Z by electrical stimulation of the contralateral thalamus.5. A lesion of nucleus Z abolished the response evoked in the contralateral post-sigmoid gyrus of the cerebral cortex by the Group I muscle afferents of the hind limb.6. A superficial transection of the ipsilateral dorsolateral fascicle at the 1st cervical segment abolished the potentials evoked in nucleus Z.7. Results of lumbar cord transections showed that most of the primary afferents of the Group I hind limb path supplying nucleus Z enter the dorsolateral fascicle at L3 level.8. The relation of the Group I hind limb path to the dorsal spinocerebellar tract is discussed.

Action Potentials↗