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2 Acta Neurobiologiae Experimentalis

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Retinal origin of electrically evoked potentials in eye-eye and eye-neck montages

100%

Foik A. , Kublik E. , Popek A. , Waleszczyk W. J.

nr Suppl.1

Noninvasive current stimulation is a rapidly developing tool for rehabilitation of visual impairment. The therapeutic use of current stimulation requires solving many technical problems including optimal placement of stimulating electrodes (SE). In this study we asked the question about origin of electrically evoked potential (EEP) and it’s dependence on the placement of the SE. In acute experiments on rats under urethane anaesthesia, visually (VEP) and electrically evoked potentials were recorded using single- and multi-channel electrodes from 5 visual structures: retina (1 channel), lateral geniculate nucleus (8 channels), superior colliculus (7 channels) and visual cortex of both hemispheres (16 channels each). Recordings of EEPs were performed to electrical pulse current stimulation, delivered using two electrodes placed either on one eye-ball (eye-eye montage) or on the eye-ball and neck (eyeneck montage). To reveal the origin of EEPs in both electrode montages 5 µl of tetrotodoxine (TTX 0.5 mM), was injected into the eye to block retinal ganglion cells’ activity and EEPs were recorded for both SE configurations. Lack of VEPs confirmed the successful block of ganglion cells’ activity. We have observed full decay of EEPs after TTX injection independent on the SE configurations. These results indicate on the retinal origin of EEPs regardless of the reference electrode placement. Supported by ERA-NET Neuron project REVIS.

Stimulus dependent oscillations in visually evoked activity of cat's superior colliculus

88%

Foik A. , Silva A. , Wypych M. , Mochol G. , Waleszczyk W. J.

tom 72

nr 2

Visual information is transferred from retina to higher order cortical areas by few parallel pathways and encoded in different ways. In this study, we focused on encoding of visual information in the superior colliculus, which is the first stage of extrageniculate pathway. One of ways in which neurons encode information is rate coding based on the change in a number of action potentials in response to stimulus presentation. The other coding scheme is temporal coding, which include information about temporal patterns of neuronal spiking, present, for example, in the form of oscillations. The aim of this study was to reveal the presence of stimulus dependent oscillations in visually evoked activity of neurons in the superficial layers of the cat’s superior colliculus. Neuronal activity was recorded from anesthetized (isoflurane in N2O/O2) animals during visual stimulation by spot of light moving in broad range of velocities as well as during presentation of light spot flashing in random locations within the receptive field of recorded neuron. Oscillations were identified by means of auto-correlation and spectral analyses. We found stimulus dependent oscillations in half of tested neurons. Moreover, oscillatory activity appeared to depend on the stimulus velocity. Different measures of oscillations strength (SO), such as z-score, oscillation score or F-statistics revealed positive correlation between SO and velocity. Stimulus dependent oscillations appeared also in responses to onset of the light spot. These results suggest importance of oscillations for processing of information about fast changes within receptive fields of neurons in the extrageniculate pathway. Supposedly presence of oscillations in responses of collicular cells can increase probability of information transfer to higher level of visual processing. Supported by NCN grant N N303 820640.