LABORATORY OF VISUAL SYSTEM
http://www.nencki.gov.pl/labs/vslab/vislab.html
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Head: Prof. Andrzej WRÓBEL, Ph.D.,D.Sc. E-mail: wrobel@nencki.gov.pl Staff: Marek BEKISZ, Ph.D. Joanna SMYDA 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.