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  • 1
    Electronic Resource
    Electronic Resource
    Asymmetry and ventral course of the human geniculostriate pathway as determined by hippocampal visual evoked potentials and subsequent visual field defects after temporal lobectomy (1982)
    Springer
    Experimental brain research 47 (1982), S. 317-328 
    Details
    ISSN: 1432-1106
    Keywords: Visual projection ; Cortex ; Geniculostriate pathway ; Hippocampus ; Temporal lobe ; Man
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Twenty-two patients with psychomotor epilepsy were implanted with depth electrodes along the axis of the mesial temporal lobe to identify an operable unilateral epileptic focus. Neuronal and field potentials were recorded in response to diffuse retinal illumination and clear short-latency responses were found in parahippocampal gyrus. These visual afferents in the mesial temporal lobe are assumed to be both from subcortical and cortical visual areas. There was a clear asymmetry in the ventral trajectory of the geniculostriate pathway as evidenced by asymmetric neuronal and field potential responses to brief flashes in right vs. left hippocampal gyrus and confirmed by a corresponding partial visual field deficit following therapeutic anterior temporal lobectomy. These results demonstrate that there is a retinotopic organization of fibers in the human geniculostriate pathway and that this pathway may have considerable variability in the anterior and ventral course these fibers take through the temporal lobe. These findings adequately account for the presence of direct projections from geniculate to hippocampal cortex and for unexpected hemianopsias with standard resections of the temporal lobe when there is a deviant detour of the geniculostriate pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239351
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  • 2
    Electronic Resource
    Electronic Resource
    Functional connections in the human temporal lobe (1990)
    Springer
    Experimental brain research 82 (1990), S. 279-292 
    Details
    ISSN: 1432-1106
    Keywords: Human temporal lobe ; Hippocampus ; Amygdala ; Subiculum ; Electrical stimulation ; Evoked potentials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Connections in the human mesial temporal lobe were investigated using brief, single pulses of electrical stimulation to evoke field potential responses in limbic structures of 74 epileptic patients. Eight specific areas within these structures were stereotactically targeted for study, including amygdala, entorhinal cortex, presubiculum, the anterior, middle and posterior levels of hippocampus and the middle and posterior levels of parahippocampal gyrus. These sites were studied systematically in order to quantitatively assess the response characteristics and reliability of responses evoked during stimulation of pathways connecting the areas. Specific measures included response probability, amplitude, latency and conduction velocities. The results are assumed to be representative of typical human limbic pathways since all recordings were made interictally and response probabilities across sites were not found to differ significantly between non-epileptogenic vs. identified epileptogenic regions. Field potentials ranging in amplitude from less than 0.1 to greater than 6.0 mV were evoked ipsilaterally, with mean onset latencies and conduction velocities ranging from 4.4 ms and 3.64 m/s in the perforant pathway connecting entorhinal cortex to anterior hippocampus to 24.8 ms and 0.88 m/s in the pathway connecting the amygdala and middle hippocampus. Stimulation of presubiculum and entorhinal cortex were most effective in evoking widespread responses in adjacent limbic recording sites, whereas posterior parahippocampal gyrus appeared functionally separated from other limbic sites since its probability of influencing ipsilateral sites was significantly lower than any other area. It was particularly noteworthy that stimulation did not evoke responses in any sites in contralateral hippocampal formation; even though a large number of sites were tested with bilateral implantation of homotopic electrodes. The absence of evidence for a functional contralateral limbic projection in the human brain stands in marked contrast to the anatomical and physiological evidence in lower animals for strong contralateral connections between subfields of the hippocampus via the hippocampal commissure. In addition, it correlates well with anatomical evidence for reduced hippocampal commissural connections in lower primates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231248
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  • 3
    Electronic Resource
    Electronic Resource
    Functional connections in the human temporal lobe (1991)
    Springer
    Experimental brain research 85 (1991), S. 174-187 
    Details
    ISSN: 1432-1106
    Keywords: Amygdala ; Entorhinal cortex ; Hippocampus ; Subiculum ; Parahippocampal gyrus ; Electrical stimulation ; Evoked potentials ; Epilepsy ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In a previous investigation of functional limbic pathways in the human mesial temporal lobe, we found evidence for strong connections between ipsilateral mesial temporal structures, but none for contralateral functional connections (Wilson et al. 1990). In the present study, we focused specifically upon the question of functional commissural linkages between these structures by systematic stimulation of a total of 390 electrode placements in 74 epileptic patients with temporal lobe depth electrodes implanted for surgical diagnosis. Eight standard electrode placement regions were targeted: amygdala, entorhinal cortex, anterior, middle and posterior hippocampus, subicular cortex, middle parahippocampal gyrus, and posterior parahippocampal gyrus. Three to six electrodes were implanted bilaterally in each patient, and each electrode was individually stimulated while recording from all the other sites. Out of the 390 electrodes stimulated, 78% were effective in evoking clear responses in adjacent ipsilateral structures, and 75% of 581 ipsilateral recording sites were responsive to stimulation. Only one of the stimulated electrode sites was effective in evoking responses in contralateral recording sites, and only two of 511 contralateral recording sites were responsive to that stimulation. The effective stimulation site was in presubicular cortex, and the responsive contralateral recording sites were in entorhinal and presubicular cortices. Response to this stimulation site was intermittent and variable in latency. The relative ease of obtaining functional verification of significant ipsilateral anatomical pathways in the human limbic system, and the sharply contrasting difficulty of functionally activating commissural pathways to contralateral limbic sites are discussed in the context of decreases in hippocampal contribution to commissural pathways in the primate brain compared to sub-primate mammals, and the significance of this change to normal limbic system function as well as to mechanisms of seizure spread in epilepsy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229999
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  • 4
    Electronic Resource
    Electronic Resource
    Kainic acid induced hippocampal seizures in rats: comparisons of acute and chronic seizures using intrahippocampal versus systemic injections (1995)
    Springer
    Neurological sciences 16 (1995), S. 39-44 
    Details
    ISSN: 1590-3478
    Keywords: temporal lobe epilepsy ; partial seizures ; synaptic reorganization ; developing seizures ; EEG/video
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Sommario L'epilessia ippocampale è una sindrome recentemente definita che si riscontra nel 65% di tutte le epilessie del lobo temporale ed è caratterizzata da: 1) esordio elettrografico (EEG) nell'ippocampo (HC) precedente l'attività EEG critica nelle altre strutture; 2) riscontro di sclerosi ippocampale e di riorganizzazione sinaptica delle fibre muscoidi nel tessuto asportato chirurgicamente; 3) regressione delle tipiche crisi parziali complesse in seguito a resezione chirurgica. Noi abbiamo iniezioni di acido cainico in ratti di diversa età postnatale (da P7 all'età adulta) per ottenere punte EEG persistenti in HC, attività EEG critica e crisi comportamentali. Il monitoraggio video-EEG ha dimostrato che in questo modello ottenuto con iniezione intraippocampale di acido cainico si osserva il progressivo sviluppo di: 1) punte EEG interittali ipsilaterali; 2) in uno stadio successivo complessi di polipunta; 3) scariche di punte EEG bilaterali asincrone; 4) crisi parziali complesse associate a scariche EEG che iniziano nell'HC di un lato e si propagano occasionalmente all'HC del lobo opposto e alla corteccia motoria; 5) riorganizzazione sinaptica delle fibre muscoidi in tutti i ratti con crisi anche se iniettati precocemente (P7). Questi risultati indicano che il modello ottenuto con iniezione intraippocampale di acido cainico è assimilabile all'epilessia ippocampale umana.
    Notes: Abstract Hyppocampal epilepsy is a recently defined syndrome occurring in 65% of all temporal lobe epilepsies as defined by: 1) electrographic (EEG) onset in the hippocampus (HC) prior to EEG seizures elsewhere, 2) post-resection hippocampal sclerosis and mossy fiber synaptic reorganizations and 3) relief of typical complex partial seizures after surgical resection of the hyppocampus. We used intrahippocampal kainic acid injections V2 in rats at different developmental ages (postnatal 7 through adult) to develop long term spontaneous HC EEG spikes, EEG seizures, and behavioral seizures. Split-screen video/EEG monitoring demonstrated that this intrahippocampal kainic acid model produced progressive development of: 1) ipsilateral interictal spikes, 2) later polyspike complexes, 3) bilaterally-asynchronous EEG spiking, 4) unilateral HC EEG seizure onsets with occasional secondarily generalized spread to apposite HC and motor cortex to elicit complex partial seizures, and 5) in all seizing rats there was mossy fiber synaptic reorganization, even when injected at age 7 days. These results indicate that the intrahippocampal kainic acid injection model is similar to human hippocampal epilepsy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02229073
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