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  • 1
    Electronic Resource
    Electronic Resource
    The contributions of position, direction, and velocity to single unit activity in the hippocampus of freely-moving rats (1983)
    Springer
    Experimental brain research 52 (1983), S. 41-49 
    Details
    ISSN: 1432-1106
    Keywords: Neurophysiology ; Single units ; Hippocampus ; Radial maze behavior ; Cognitive maps ; Place cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Isolated single units in rat dorsal hippocampus and fascia dentata were classified as ‘Theta’ or ‘Complex-Spike’ cells, and their firing characteristics were examined with respect to position, direction and velocity of movement during forced choice, food rewarded search behavior on a radial eight arm maze. Most spikes from CS cells ocurred when the animal was located within a particular place on the maze and moving in a particular direction. Theta cells had very low spatial selectivity. Both cell categories had discharge probabilities which increased somewhat as a function of running velocity but tended to asymptote well before half-maximal velocity. The place/direction specificity of CS cells was significantly higher in CA1 than in CA3 and CA3 CS cells exhibited a striking preference for the inward radial direction. The pronounced directional selectivity of CS cells, at least in the present environment, suggests that they fire in response to complex, but specific, stimulus features in the extramaze world rather than to absolute place in a non-egocentric space. An alternative possibility is that the geometrical constraints of the maze surface have a profound influence on the shapes of the response fields of CS cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00237147
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Hippocampal granule cells are necessary for normal spatial learning but not for spatially-selective pyramidal cell discharge (1989)
    Springer
    Experimental brain research 76 (1989), S. 485-496 
    Details
    ISSN: 1432-1106
    Keywords: Hippocampus ; Single units ; Place cells ; Colchicine ; Spatial behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of massive destruction of granule cells of the fascia dentata on the spatial and temporal firing characteristics of pyramidal cells in the CA1 and CA3 subfields of the hippocampus were examined in freely moving rats. Microinjections of the neurotoxin colchicine were made at a number of levels along the septo-temporal axis of the dentate gyri of both hemispheres, resulting in destruction of over 75% of the granule cells. By contrast there was relatively little damage to the pyramidal cell fields. As assessed by three different behavioral tests, the colchicine treatment resulted in severe spatial learning deficits. Single units were recorded from the CA1 and CA3 subfields using the stereotrode recording method while the animals performed a forced choice behavioral task on the radial 8-arm maze. Considering the extent of damage to the dentate gyrus, which has hitherto been considered to be the main source of afferent information to the CA fields, there was remarkably little effect on the spatial selectivity of “place cell” discharge on the maze, as compared to recordings from control animals. There was, however, a change in the temporal firing characteristics of these cells, which was manifested primarily as an increase in the likelihood of burst discharge. The main conclusion derived from these findings is that most of the spatial information exhibited by hippocampal pyramidal cells is likely to be transmitted from the cortex by routes other than the traditional “trisynaptic circuit”. These routes may include the direct projections from entorhinal layers II and III to CA3 and CA1, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248904
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Behavioral correlates of theta-on and theta-off cells recorded from hippocampal formation of mature young and aged rats (1990)
    Springer
    Experimental brain research 80 (1990), S. 365-373 
    Details
    ISSN: 1432-1106
    Keywords: Hippocampus ; Theta cells ; Place fields ; Movement correlates ; Spatial performance ; Rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Most hippocampal formation single units in freely behaving rats fall into one of two categories (Ranck 1973). The most obvious behavioral correlate of complex-spike (CS) cells is spatially selective discharge (O'Keefe and Dostrovsky 1971), while theta cells show increased firing in phase with the EEG θ rhythm associated with Vanderwolf's Type I behaviors (e.g. walking, exploration). Recently, Colom and Bland (1987) described, in urethane anesthetized animals, a class of non-CS cell which was inactive in the presence of EEG θ and discharged continuously during LIA. They called these “theta-off” cells and used the term “theta-on” to refer to the classical “theta” cell. We describe the behavioral correlates of 14 theta-off cells encountered in CA1 (n = 1), hilus fascia dentata (FD; n = 4), subiculum (n = 6), and entorhinal cortex (n = 3). These cells were encountered very infrequently in the course of several experimental investigations of mature young and old rats involving 885 hippocampal neurons recorded from 33 rats during radial maze performance. Fourteen theta-on cells encountered within a few hundred microns of the sites where theta-off cells were recorded were included for comparison. Both theta-on and theta-off cells discharged single spikes and did not show CS bursting characteristic of pyramidal cells. Theta-off cells, however, exhibited significantly greater spike durations than theta-on cells. Mean rates for theta-on and theta-off cells were 8.7 Hz and 6.5 Hz, respectively. Maximum rates were 114 Hz and 104 Hz, respectively. Some cells of both types showed 6–8 Hz modulation while animals traversed the maze. Whereas firing rate for theta-on cells increased smoothly with running velocity, it decreased smoothly for theta-off cells. While no theta-on cells exhibited clear spatial selectivity, two hilar theta-off cells did. When EEG θ rhythm was temporarily abolished by local injection of tetracaine into the medial septum, two theta-off cells were observed to fire continuously at high rates irrespective of behavior, with a pronounced 18–20 Hz rhythmic modulation. Under these circumstances, theta-on cells decrease their rates. Within the 7 theta-off cells recorded in each of the two age groups, there were no statistically significant differences in firing characteristics. Possible anatomical candidates for theta-off cells are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00228163
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    Paper (German National Licenses)
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