3 results
GABA-induced inactivation of functionally characterized sites in cat striate cortex: Effects on orientation tuning and direction selectivity
- John M. Crook, Zoltan F. Kisvárday, Ulf T. Eysel
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- Journal:
- Visual Neuroscience / Volume 14 / Issue 1 / January 1997
- Published online by Cambridge University Press:
- 02 June 2009, pp. 141-158
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Microiontophoresis of γ-aminobutyric acid (GABA) was used to reversibly inactivate small sites of defined orientation/direction specificity in layers II-IV of cat area 17 while single cells were recorded in the same area at a horizontal distance of ~350–700 jam. We compared the effect of inactivating iso-orientation sites (where orientation preference was within 22.5 deg) and cross-orientation sites (where it differed by 45–90 deg) on orientation tuning and directionality. The influence of iso-orientation inactivation was tested in 33 cells, seven of which were subjected to alternate inactivation of two iso-orientation sites with opposite direction preference. Of the resulting 40 inactivations, only two (5%) caused significant changes in orientation tuning, whereas 26 (65%) elicited effects on directionality: namely, an increase or a decrease in response to a cell's preferred direction when its direction preference was the same as that at an inactivation site, and an increase in response to a cell's nonpreferred direction when its direction preference was opposite that at an inactivation site. It is argued that the decreases in response to the preferred direction reflected a reduction in the strength of intracortical iso-orientation excitatory connections, while the increases in response were due to the loss of iso-orientation inhibition. Of 35 cells subjected to cross-orientation inactivation, only six (17%) showed an effect on directionality, whereas 21 (60%) showed significant broadening of orientation tuning, with an increase in mean tuning width at half-height of 126%. The effects on orientation tuning were due to increases in response to nonoptimal orientations. Changes in directionality also resulted from increased responses (to preferred or nonpreferred directions) and were always accompanied by broadening of tuning. Thus, the effects of cross-orientation inactivation were presumably due to the loss of a cross-orientation inhibitory input that contributes mainly to orientation tuning by suppressing responses to nonoptimal orientations. Differential effects of iso-orientation and cross-orientation inactivation could be elicited in the same cell or in different cells from the same inactivation site. The results suggest the involvement of three different intracortical processes in the generation of orientation tuning and direction selectivity in area 17: (1) suppression of responses to nonoptimal orientations and directions as a result of cross-orientation inhibition and iso-orientation inhibition between cells with opposite direction preferences; (2) amplification of responses to optimal stimuli via iso-orientation excitatory connections; and (3) regulation of cortical amplification via iso-orientation inhibition.
Pharmacological inactivation of pretectal nuclei reveals different modulatory effects on retino-geniculate transmission by X and Y cells in the cat
- Klaus Funke, Ulf T. Eysel
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- Journal:
- Visual Neuroscience / Volume 12 / Issue 1 / January 1995
- Published online by Cambridge University Press:
- 02 June 2009, pp. 21-33
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The modulatory influence of pretectal neurons on retino-geniculate transmission in the cat was studied by cross-correlation analysis of single-unit activity simultaneously recorded from the dorsal lateral geniculate nucleus (dLGN) and the pretectum (PT) and with reversible inactivation of the PT by GABA microiontophoresis during simultaneous visual stimulation of PT and dLGN neurons. Visually induced population activity in PT nuclei was achieved by a moving (or counterphasing) grating which was presented in the background of the light spot used to stimulate the dLGN neuron. As a control, the light spot was presented on a stationary grating to avoid stimulation of PT neurons but to yield the same illumination of the background. Extracellularly recorded dLGN relay cells of the X- and Y-type were found to be differentially affected by the PT-dLGN projection. During visual stimulation of PT cells, X cells were strongly inhibited and this effect was significantly reduced during PT inactivation. By contrast, the visual responses of most Y cells were affected neither by PT stimulation nor by PT inactivation. In addition, the temporal structure of spike patterns during the light response was examined with autocorrelograms and spike-interval distributions. X-on cells often exhibited a multimodal interval distribution and oscillatory type of activity. During stimulation of the PT interval distributions changed in a characteristic manner and oscillations disappeared. Both effects could be almost totally cancelled by PT inactivation. By contrast, the temporal structure of Y-cell responses was not affected. Our results demonstrate for the first time a pretectal modulation of retino-geniculate transmission in cat dLGN which is clearly different for X and Y cells. This influence seems to be mediated via (inhibitory) interneurons, since we found no indication for a direct coupling between PT and dLGN units. This projection might contribute to the well-known phenomenon of saccadic suppression.
Inverse correlation of firing patterns of single topographically matched perigeniculate neurons and cat dorsal lateral geniculate relay cells
- KLAUS FUNKE, ULF T. EYSEL
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- Journal:
- Visual Neuroscience / Volume 15 / Issue 4 / April 1998
- Published online by Cambridge University Press:
- 01 April 1998, pp. 711-729
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Action potentials of single perigeniculate (PGN) cells and relay cells of the dorsal lateral geniculate nucleus (dLGN) with topographically matched or at least partially overlapping receptive fields (RF) were simultaneously recorded in the anesthetized and paralyzed cat during visual stimulation with moving gratings or flashing light spots of different size. In many cases, PGN cells showed an activity pattern which appeared like a mirror image of distinct periods of dLGN activity. Flashing spots evoked transient volleys of activity in PGN cells which increased in strength and shortened in latency with increasing size of the stimulus. These responses were temporally matched with inhibitory phases in the early part of visual responses in the dLGN. The spatio-temporal properties of the RFs were established by reverse correlation of the spike activity with the spatially random presentation of bright and dark spots within an array of 20 × 20 positions. Anticorrelated firing patterns of such kind could also be elicited as interocular inhibition with stimulation of the perigeniculate RF in the nondominant eye. Inversely correlated changes in spontaneous and visually induced activity were also visible during spontaneous changes in EEG pattern. With increasing synchronization of the EEG (predominance of delta-waves) the strength of geniculate visual responses declined while maintained perigeniculate activity increased. A weakened interocular and monocular inhibition of dLGN relay cells during visual stimulation of PGN RFs could be achieved with local reversible inactivation of PGN areas topographically matched with the dLGN recording sites. The results indicate that the PGN contributes to the state-dependent control of retino-geniculate transmission and to the monocular and interocular inhibitory processes that shape the visual responses in the dLGN.