LABORATORY OF VISUAL SYSTEM

http://www.nencki.gov.pl/labs/vslab/vislab.html

| Head: Prof. Andrzej WRÓBEL, Ph.D.,D.Sc. E-mail: wrobel@nencki.gov.pl Staff: Marek BEKISZ, Ph.D. Anaida GHAZARYAN, Ph.D. Ewa KUBLIK, M.D., Ph.D. Wioletta WALESZCZYK, Ph.D. Joanna SMYDA Wojciech BORKOWSKI Ph.D. student Daniel ŚWIEJKOWSKI, M.D. Graduate students: Marek Wypych Piotr Leszczyński

Current research in the laboratory focuses on understanding dynamic operations within sensory systems of behaving animals. Using electrophysiological recording techniques and neuroinformatic methods for data analysis, we are trying to correlate the specific activation of studied neuronal networks with their behavioral context. Three parallel projects are under investigation:

1. Electrophysiological correlates of visual attention.

In agreement with the old hypothesis that the descending feedback projections in the visual system might be activated during attention processes, we have shown in the cat that, (1) cortico-geniculate feedback has a built-in potentiation mechanism acting at the beta frequency -- by means of this mechanism the thalamic cells may be activated and consequently lower the threshold for transmission of visual information; (2) the enhanced beta activity, as shown by chronic local field potential recordings (see Fig.1), is propagated along the feedback pathway solely during attentive visual behavior; (3) this attention-related activity consists of 100-350 ms long bursts which appear simultaneously in cortical and thalamic sites that are involved in central vision and both also correlate in time with gamma oscillatory events; (4) such bursting activity spreads to all investigated visual centers, including the lateral posterior-pulvinar complex and higher cortical areas; (5) the idle beta oscillatory rhythm observed in the number of visual structures during non-visual stimulation changes towards a specific pattern of synchronization during attentive seeing. Similar data is obtained during visual behavior in humans.

We suggest that the observed pattern of beta activity represents the temporarily activated mosaic of functional connections needed for current visual scan. For example, it may produce the background activation for gamma synchronization and perception. Our hypothesis for the role of the cortico-thalamic pathways in attentive perception may be easily applied to all stages of visual and possibly other sensory processing.

Figure 1. (A) Averaged amplitude spectra calculated from signals recorded from cat's visual cortex during increased visual (thick line) and auditory (thin line) attention in the same experimental session. Each spectrum was obtained from 14 independent signal epochs of 2.5 s duration, taken from successfully ended trials; (B), Comparison of averaged LFP amplitude spectra from the time periods preceding correct and erroneously ended behavioral responses in the same session; (C), (D), amplitude spectra showing spectral content of the signal registered from the primary visual (C) and auditory (D) cortices of other cat, calculated from correct trials in one experimental session. Stars indicate the significanct differences in the beta band (t-test, P<0.05). In the frequency spectra of the visual cortex activity, calculated for both animals before the correct response, the amplitude of the beta band is significantly higher than in the spectra calculated for auditory and erroneous visual trials. In the spectrum obtained from the auditory cortex, amplitude of the beta band is significantly higher during auditory than visual trials (from Bekisz and Wróbel 1993).

2. Information processing in the cortico-thalamic part of the somatosensory system.

In order to study the context-dependent gating of the sensory information at the cortical level of the whisker-barrel system we have shown in the rat that: (1) evoked potentials (EPs) to vibrissa stimulation can be divided into two distinct classes according to the relative contribution of their principal components; (2) these components can be attributed to the activation of two pyramidal cell populations: supra- and infragranular; (3) with well-habituated stimuli EPs are dominated by a component related to the supragranular cells. The first reinforcement of vibrissa stimulation in the classical aversive paradigm favours the appearance of EPs dominated by a component characteristic of infragranular cells which match the activation of the medial part of thalamic posterior nuclear complex (POm) and the surround zone of the barrel field; similar dynamic changes of the relative occurrence of the two EP classes follow other aversive stimuli, including pressing the animal's ear and restraining a whisker; (4) the enhanced EPs were preceded by a short lasting voltage shift of local field potentials which might be partly due to cholinergic inputs from the basal forebrain.

We hypothesize that neuromodulatory action elicited by contextual stimulation activates all neurons in the principal barrel column, including those providing an output to the surrounding barrels. In the classical conditioning paradigm this dynamic mechanism may lead to experience-dependent changes within the intracortical network.

3. Mechanisms of movement detection in vision (experiments in acute cat preparation).

Investigations on superior colliculus have shown that receptive fields of collicular neurons are composed of subregions with different direction-response profiles. We hypothesize that such neurons can be involved in multiple synchronized networks participating in detection of diverse stimulus attributes. In collaboration with B. Dreher’s laboratory experiments studied the functional role of different visual channels in the velocity response profiles of collicular neurons. Extracellular single unit recording was used to examine the effect of selective conduction-block of the Y-type fibers in optic nerve on properties of the receptive fields of neurons in the cat’s superior colliculus. This research has shown that: (1) there was a substantial degree of excitatory convergence of Y- and non-Y-information channels on single neurons in the superior colliculus and that (2) the responses to visual stimuli moving with high velocity depended on the integrity of the Y-channel.

4. Plasticity in the visual system following retinal lesions.

Investigations of plasticity in the cat’s visual cortex following the monocular circumscribed retinal lesions are carried out in collaboration with B. Dreher’s and M. Calford’s laboratories. We have shown that (1) damage to the part of the retina induced topographic reorganization of the primary visual cortices (area 17 and 18) such that neurons in the lesion projection zone could be activated from regions of the normal retina adjacent to the lesion. (2) In both adult-lesioned and kitten-lesioned animals, the receptive fields’ properties of binocular neurons located in lesion projection zone in area 17, such as receptive field sizes, preferred orientations and preferred stimulus velocities for stimuli presented via the ectopic receptive fields, were not significantly different from those for stimuli presented via their normal counterparts. (3) In kitten–lesioned animals, the upper cut-off velocities for stimuli presented via the ectopic receptive fields were also not significantly different from those for stimulation via the normal receptive fields, but were lower in cats lesioned in adulthood. (4) The age of lesion related laminar differences in ocular dominance of lesion projection zone neurons were observed. Differences in the properties of lesion projection zone cells in kitten-lesioned and adult-lesioned indicate substantial differences in the degree of cortical plasticity between adult and adolescent cats.

Selected publications:

1. A. Wróbel. Beta activity: a carrier for visual attention. Acta Neurobiol. Exp., 2000, 60: 247-260.

2. Bekisz M., Wróbel A. 2003. Attention-dependent coupling between beta activities recorded in the cat's thalamic and cortical representations of the central visual field. Europ. J. Neurosci. 17: 421-426.

3. A. Wróbel, E. Kublik, P. Musiał. Gating of the sensory activity within barrel cortex of the awake rat. Exp. Brain Res., 1998, 123: 117-123.

4. Musiał, P., Kublik, E., and Wróbel, A. 1998. Spontaneous variability reveals principal components in cortical evoked potentials. Neuroreport 9: 2627-2631.

5. Kublik E., Musiał P., Wróbel A. 2001. Identification of principal components in cortical evoked potentials by brief surface cooling. Clin. Neurophys. 112: 1720-1725.

6. Waleszczyk W. J., Wang C., Burke W. and Dreher B. (1999) Velocity response profiles of collicular neurons: parallel and convergent visual information channels. Neuroscience 93: 1063-1076.

7. Wang C., Waleszczyk W.J., Benedek, G., Burke W., Dreher B. (2001) Convergence of Y and non-Y channels onto single neurons in the superior colliculi of the cat. NeuroReport 12: 2927 - 2933.).

8. Dec K., Waleszczyk W.J., Wróbel A., Harutiunian-Kozak B.A. (2001) The spatial substructure of visual receptive fields in the cat’s superior colliculus. Arch. Ital. Biol. 139: 337-355.

9. Waleszczyk W.J., Wang C., Young J.M., Burke W., Calford M.B., Dreher B. (2003). Laminar differences in plasticity in area 17 following retinal lesions in kittens or adult cats. Eur. J. Neurosci. 17: in press.