Project 1: Investigation of the neural circuits subserving visual perception and attention

Supervised students

H. Bahmani (Neural Correlates of Binocular Rivalry in Parietal Cortex)

F.A.C. Azevedo (Effects of attention on neural processing in the striate cortex of non-human primates)

Q. Li (Neuronal Population Activity Underlying Multi-Stable Motion Perception)

Introduction and Scientific Aims

The spontaneous perceptual alternations experienced when viewing certain type of visual stimuli, e.g. the Necker cube or Rubin’s faces-and-vase illusion, offer an excellent opportunity to discern neural activity related to conscious perception from that underlying sensory information processing.  Initial electrophysiological studies of multistable perception were performed in feature and object selective areas, i.e. in the temporal visual pathway, and demonstrated a widespread inter-areal network of neurons that modulate their activities according to their preferences and as well as according to which stimulus is perceived or suppressed [1-3]. Yet, fMRI studies indicated that areas with little or no pattern selectivity within the spatial-information processing dorsal pathway might also be involved in multistable perception, and particularly in the initiation of perceptual reversals [4]. Yet, not surprisingly, the mechanisms inducing perceptual alternations and temporary coherent percepts remain unclear. Unclear is also the role of attention and other neuromodulatory processes that may influence perceptual reorganization. Combined physiology and MR imaging is a promising approach for tackling such questions at the neural population, that is, they permit assessment of effective inter-area connectivity and study of local physiological responses. Our goal in this project is to study the mechanisms that select, extract, and bind together the visual features presented in multistable displays into coherent visual percepts, and the way such mechanisms are affected by attention.

Methods

We perform multi-electrode (tetrodes, laminar probes) [5] recordings in awake, behaving non-human primates (Macaca mulatta) trained to report their subjective perception during the presentation of multistable stimuli like binocular rivalry and motion plaids (Fig. 1 A). These stimuli yield clearly distinct perceptual states and allow parametric control over the relative probability of different percepts. In some animals, we also employ simultaneous recording of electrophysiological signals and fMRI while they perform spatial attention tasks in high field scanners (Fig. 1 B) [6]. Our analysis approaches include neural population decoding, measurements of synchrony and coherence between single unit activity (SUA) and local field potentials (LFP), probabilistic inference and theoretical modeling.

Results and Preliminary Conclusions

Electrophysiological recordings in the lateral intraparietal area (LIP) indicate a potential role of this area in perceptual transitions during binocular rivalry. The recorded units typically showed an initial burst of activity around perceptual transitions both during congruent and incongruent stimulation (Fig. 1 C). Importantly, these sharp transients are eliminated in conditions where physical changes that do not induce a concomitant change in perception are introduced in the stimuli. The transient response of the recorded neurons typically has a short latency and is then followed by a separate sustained response that exhibits independent dynamics. While the initial transient response is almost always excitatory the sustained responses are excitatory in some cells and suppressive in others. Interestingly, the sustained responses during incongruent stimulation were clearly suppressed in comparison to congruent conditions (Fig. 1 D).  We speculate that the transient and sustained responses may reflect two separate underlying processes. The short latency response may reflect a fast sensory integration signal in a bottom-up manner, while the sustained activity may represent top-down influences originating from higher areas in the prefrontal cortex.

It follows that areas at the high end of the dorsal pathway may be involved in multistable perception in a different way in comparison with feature and object selective areas of the ventral visual stream. While a hierarchically increasing percentage of feature selective neurons in the ventral pathway modulate their activities in parallel with perception of their preferred and non-preferred patterns, parietal areas might perform substantially different functions like integrating information from different spatial locations and signaling its binding into a coherent percept. Our preliminary results from electrophysiological recordings in LIP suggest that a transient signal is present only when there is a concomitant change in perception. This transient signal might provide a trigger for constellations of feature selective units in the ventral pathway to reorganize their patterns of activation leading to a perceptual switch. In addition, the suppression of the sustained responses during incongruent stimulation may indicate inhibitory processes underlying the competition between different stimulus representations at higher order areas.

References

1.         Ungerleider LG, Galkin TW, Mishkin M (1983) Visuotopic organization of projections from striate cortex to inferior and lateral pulvinar in rhesus monkey, J Comp Neurol 217(2) 137-57.

2.         Leopold, D.A., and Logothetis, N.K. (1999) Multistable phenomena: changing views in perception, Trends Cogn Sci 3, 254-264.

3.         Keliris GA, Logothetis NK, and Tolias AS (2010) The role of the primary visual cortex in perceptual suppression of salient visual stimuli. J Neurosci 30, 12353-12365.

4.         Lumer ED, Friston KJ, and Rees G (1998) Neural correlates of perceptual rivalry in the human brain Science 280, 1930-1934.

5.         Tolias AS, Ecker AS, Siapas AG, Hoenselaar A, Keliris GA and Logothetis NK (2007) Recording Chronically from the same Neurons in Awake, Behaving Primates Journal of Neurophysiology 98(6) 3780-3790.

6.         Keliris GA, Shmuel A, Ku S, Pfeuffer J, Oeltermann A, Steudel T, and Logothetis NK (2007) Robust controlled functional MRI in alert monkeys at high magnetic field: effects of jaw and body movements Neuroimage 36 (3) 550-570.

Figure 1 We train non-human primates to report their subjective perception during presentation of bistable stimuli through a mirror steroscope (A). In some experiments we perform simultaneous recordings of electrophysiological and fMRI signals in high field scanners while modulating the attentional state of the subjects (B). Comparison between two experimental conditions (C) demonstrates strong suppression during incongurent in comparison to congruent stimulation (D).

Project 2: Studies of cortical reorganization after injury in human and non-human primates

(funded by the 7^th Framework Program of the European Commission – Plasticise project)

Supervised students

Y. Shao (Visual cortical plasticity after V1 lesion and retina degeneration in macaque monkeys)

A. Papanikolaou (Population receptive field mapping in human subjects with visual cortical lesions)

Collaborators

Dr. S. Lee (Estimation of population receptive fields in the human visual cortex)

Prof. Dr. S.M. Smirnakis (Baylor Collage Medicine, Houston, TX)

Prof. Dr. med. Ulrich Schiefer (Institute for Ophthalmic Research, UKT, Tuebingen)

Introduction and Scientific Aims

Damage to the visual cortex as a result of stroke or other brain diseases can lead to a loss of conscious vision in part(s) of the visual field introducing a tremendous burden to the individual. While the ability of the cortex to reorganize after injury has been convincingly demonstrated in the somatosensory, motor and language domains, evidence for reorganization in the visual cortex remains controversial with some studies suggesting extensive reorganization [1] while others find little if any changes [2, 3]. Further understanding of the reorganization capabilities of the visual system is central in the search for options of rehabilitation and recovery. We aim to study cortical reorganization after central nervous system injury in the visual system of human and non-human primates to understand: a) how is retinotopic organization of early visual cortical areas changing after visual cortex injury, b) if and how the receptive fields of neurons in the healthy cortex are changing, and c) how is sensitivity to motion in visual areas (deprived from their major input) changing. Initially we evaluate the degree to which the above changes happen spontaneously. Our long-term goal is to develop and assess specific training strategies that can invoke and/or enhance useful reorganization in the visual system and ultimately increase the patients’ quality of life.

Methods

Currently, we perform fMRI experiments both in human and non-human primates (rhesus macaques) to map visual response properties in a number of visual areas. Our visual stimulation paradigms include retinotopic mapping using moving bar stimuli that can be also used to estimate the aggregate receptive field sizes of fMRI voxels with the pRF method [4]. In addition, we use full field flickering white noise stimuli that stimulate differentially the spatio-temporal components of the receptive fields providing additional information for the responses of these populations of cells. At a second stage we will introduce cortical lesions in primary visual cortex of rhesus macaques and study visual reorganization at the electrophysiological level.

Results and Preliminary Conclusions

We find that the retinotopic maps of the spared early visual areas in patients with cortical lesions remain stable in comparison to control subjects (Fig. 1 A-B). In some subjects we observed some changes in the response properties of higher visual areas like V3A and hV5/MT+. In monkeys, we were able to reproduce accurate retinotopic maps and receptive field sizes agreeing with previous electrophysiological investigations (Fig. 1 C-D). Our preliminary results indicate that no significant reorganization happens spontaneously in early visual areas after injury

References

1.       Baker CI, Peli E, Knouf N, Kanwisher NG (2005) Reorganization of visual processing in macular degeneration J Neurosci 25(3):614-8.

2.       Sunness JS, Liu T, Yantis S. (2004) Retinotopic mapping of the visual cortex using functional magnetic resonance imaging in a patient with central scotomas from atrophic macular degeneration Ophthalmology 111(8):1595-8.

3.       Smirnakis SM, Brewer AA, Schmid MC, Tolias AS, Schuz A, Augath M, Inhoffen W, Wandell BA, Logothetis NK (2005) Lack of long-term cortical reorganization after macaque retinal lesions Nature 435(7040):300-7.

4.       Dumoulin SO, Wandell BA (2008) Population receptive field estimates in human visual cortex Neuroimage 39(2):647-60.

Figure 1 We use retinotopic mapping and particularly the pRF method [4] to map receptive field properties both in human (A-B) and non-human primates (C-D). Panels A, C present color coded maps of the populations receptive field sizes in early visual areas on flattened cortical surfaces. Panels B, D demonstrate that population receptive fields increase linearly with eccentricity in different visual areas.

Georgios A. Keliris, Ph.D.

Project Leader

Max Planck Institute for Biological Cybernetics

Physiology of Cognitive Processes

Spemannstrasse 38

Tübingen, 72076

Germany

Tel.: +49 7071 601-695

E-mail: georgios.keliris@tuebingen.mpg.de

Web: http://www.kyb.tuebingen.mpg.de/~george

Ph.D. Neural and Behavioral Sciences, 2008

Max-Planck Institute for Biological Cybernetics

(Laboratory of Prof. Dr. Nikos K. Logothetis)

International Max Planck Research School,

University of Tübingen, Germany

M.Sc. Neural and Behavioral Sciences, 2003

International Max Planck Research School,

University of Tübingen, Germany

B.Sc. Physics, 2000

University of Cyprus

Nov 2007                    Ph.D. Thesis: “Investigating the Neural Correlates of Visual Perception” Supervisors: Prof. Dr. Nikos K. Logothetis, Dr. Andreas S. Tolias

Feb 2003                     M.Sc. Thesis: “Evaluation of Single Unit Isolation: Tetrode Recordings in Awake Behaving Macaques” Supervisor: Dr. Andreas S. Tolias

June 2000                   B.Sc. Thesis: “Strategies for the search of the HIGGS boson in the CMS experiment. Fission channel: Higgs to two photons.” (in Greek) Supervisor: Prof. Dr. Panos Razis

June 1998                                   “Early Academic Performance Award” for the best performance in the core subjects of the Degree in Physics, University of Cyprus

June 2000                                   “First Award” of the Faculty of Physics, University of Cyprus, for finishing 1^st in the ranking of the Faculty

Jan 2001 – Oct 2001                Stipendium by the Max-Planck Gesellschaft

Oct 2001 – Oct 2002                Scholarship by the DAAD for further academic study and training

2002 – 2005                               Scholarship by the Max-Planck Gesellschaft for Doctoral studies

2008 – 2009                               Post-doctoral fellowship scholarship by the Max-Planck Gesellschaft

June 2009 – Nov 2012             Post-doctoral fellowship from the ERC FP7 (Plasticise project)

May 2010 – July 2015             Principal investigator in a project of the Bernstein center for computational neuroscience (BCCN) Tuebingen

Feb 2001 – Sep 2001               Program developing for optimal visualization of the brain data collected by MEG and fMRI

MEG Center, University of Tübingen

Dr. Christoph Braun, Dr. Nikolaus Weiskopf

Sep 2001 – Feb 2002               Human fMRI studies of the perceptual filling-in

Max Planck Institute for Biological Cybernetics

Dr. Stelios Smirnakis, Dr. Zoe Kourtzi

Feb 2002 – Aug 2002               Connectivity of networks derived from firing properties of simulated neurons

Gatsby Computational Neuroscience Unit, University College London

Prof. Dr. Peter Dayan

Aug 2002 – Feb 2003               Neural basis of decisions: fMRI studies in macaques

Max Planck Institute for Biological Cybernetics

Dr. Andreas S. Tolias

June 2012 – Aug 2012             The role of attention in center-surround interactions in the visual cortex

Brain Science Institute, RIKEN, Japan

Prof. Dr. Justin L. Gardner

Maier A, Panagiotaropoulos TI, Tsuchiya N, Keliris GA

Introduction to research topic - Binocular rivalry: a gateway to studying consciousness

Front Hum Neurosci (in press)

Fischer DM, Zobor D, Keliris GA, Shao Y, Seeliger MW, Haverkamp S, Jägle H, Logothetis NK, Smirnakis SM (2012)

Detailed functional and structural characterization of a macular lesion in a rhesus macaque.

Doc Ophthalmol. 2012 Aug 26. [Epub ahead of print]

Stoewer S, Goense J, Keliris GA, Bartels A, Logothetis NK, Duncan J, Sigala N (2012)

An analysis approach for high-field fMRI data from awake non-human primates.

PLoS One. 2012; 7(1)

Stoewer S, Goense J, Keliris GA, Bartels A, Logothetis NK, Duncan J, Sigala N (2011)

Realignment strategies for awake-monkey fMRI data.

Magn Reson Imaging. 2011; 29(10):1390-400

Keliris GA, Logothetis NK, Tolias AS (2010)

The role of the primary visual cortex in perceptual suppression of salient visual stimuli.

J Neurosci. 2010; 30(37):12353-65

Ecker AS, Berens P, Keliris GA, Bethge M, Logothetis NK, Tolias AS (2010)

Decorrelated neuronal firing in cortical microcircuits.

Science. 2010; 327(5965):584-7

Berens P, Keliris GA, Ecker AS, Logothetis NK, Tolias AS (2008)

Feature selectivity of the gamma-band of the local field potential in primate primary visual cortex.

Front Neurosci. 2008; 2(2):199-207

Berens P, Keliris GA, Ecker AS, Logothetis NK, Tolias AS (2008)

Comparing the feature selectivity of the gamma-band of the local field potential and the underlying spiking activity in primate visual cortex.

Front Syst Neurosci. 2008; 2:2

Tolias AS, Ecker AS, Siapas AG, Hoenselaar A, Keliris GA, Logothetis NK (2007)

Recording chronically from the same neurons in awake, behaving primates

J Neurophysiol. 2007; 98(6):3780-90

Keliris GA, Shmuel A, Ku SP, Pfeuffer J, Oeltermann A, Steudel T, Logothetis NK (2007)

Robust controlled functional MRI in alert monkeys at high magnetic field: effects of jaw and body movements. Neuroimage. 2007; 36(3):550-70

Pfeuffer J, Shmuel A, Keliris GA, Steudel T, Merkle H, Logothetis NK (2007)

Functional MR imaging in the awake monkey: effects of motion on dynamic off-resonance and processing strategies.

Magn Reson Imaging. 2007; 25(6):869-82

Tolias AS, Keliris GA, Smirnakis SM, Logothetis NK (2005)

Reply to "Motion processing in macaque V4"

Nat. Neurosci. 2005; 8(9):1125

Moutoussis K, Keliris GA, Kourtzi Z, Logothetis NK (2005)

A binocular rivalry study of motion perception in the human brain.

Vision Res. 2005; 45(17):2231-43

Tolias AS, Keliris GA, Smirnakis SM, Logothetis NK (2005)

Neurons in macaque area V4 acquire directional tuning after adaptation to motion stimuli.

Nat Neurosci. 2005; 8(5):591-3

Panagiotaropoulos TI, Logothetis NK, Keliris, GA (in press)

Neural approaches to perceptual organization.

The Handbook of Computational Perceptual Organization (Eds. Gepshtein-Maloney)

Special Research Topic in Frontiers in Human Neuroscience

Binocular Rivalry: A Gateway to Consciousness

(co-hosted with A. Maier , T.I. Panagiotaropoulos, N. Tsuchiya)

May 2007 – Feb 2009        Daniel Lebrecht

Master’s thesis:  “Correlates of perception in primate primary visual cortex”) – now Ph.D. student with Prof. Dr Anthony Holtmaat at University of Geneva

Aug 2009 – Oct 2009         Kristin Herper

Lab rotation:  “Binocular receptive field mapping after adaptation”

Feb 2011 – Apr 2011          Pooja Viswanathan

Lab rotation: “Spike-LFP phase locking across frequency bands under different task conditions” – now Ph.D. student at University of Tuebingen.

Nov 2011 – Aug 2012        J Kausik Lakshminarasimhan

Master’s thesis: “Neuronal gamma-band synchronization in macaque area V1 follows changes in firing rate during monocular stimulation”. – now Ph.D. student at Baylor College of Medicine, Houston, TX

Jun 2009 – to date              Yibin Shao (Ph.D. student ) - co-supervised with Prof. Stelios Smirnakis (Baylor)

Project title: “Visual cortical plasticity after V1 lesion and retina degeneration in macaque monkeys”

Sep 2009 – to date              Hamed Bahmani (Ph.D. student)

Project title: “The role of parietal visual cortex in perceptual transitions during bistable perception”

Nov 2009 – to date             Amalia Papanikolaou (Ph.D. student) - co-supervised with Prof. Smirnakis (Baylor)

Project title: “Visual cortex reorganization in human subjects with cortical lesions”

Feb 2010 – to date              Frederico A. C. Azevedo (Ph.D. student) – funded by DAAD

Project title: “Effects of attention on neural processing in the striate cortex on non-human primates: a simultaneous electrophysiology fMRI study”

Apr 2011 – to date              Qinglin Li (Ph.D. Student) – funded by BCCN Tuebingen

Project title: “Neuronal population activity underlying multi-stable motion perception”

Neuron

Neuroimage

Journal of Neuroscience

PNAS

Frontiers in Human Neuroscience

Netherlands Organization for Scientific Research (NWO)

2011- to date:      Frontiers in Human Neuroscience (Associate)

Society for Neuroscience (SfN)

Vision Science Society (VSS)

Federation of European Societies for Neuroscience (FENS)

Smirnakis S.M. , Keliris G.A., Shao Y. , Papanikolaou A.  and Logothetis N.K. (August-2012): Population receptive field measurements in macaque visual cortex, 12th Annual Meeting of the Vision Sciences Society (VSS 2012), Naples, FL, USA, Journal of Vision, 13(9) 1397.

Bahmani H. , Logothetis N.K . and Keliris G.A. (August-2012): The role of parietal visual cortex in perceptual transitions during bistable perception, 12th Annual Meeting of the Vision Sciences Society (VSS 2012), Naples, FL, USA, Journal of Vision, 12(9) 683.

Papanikolaou A., Keliris G.A. , Shao Y. , Krapp E. , Papageorgiou E. , Schiefer U. , Logothetis N.K.  and Smirnakis S.M. (November-2011): Population receptive field mapping in human subjects with lesions of the visual cortex, 41st Annual Meeting of the Society for Neuroscience (Neuroscience 2011), Washington, DC, USA.

Shao Y., Keliris G.A. , Papanikolaou A. , Augath M. , Logothetis N.K.  and Smirnakis S.M. (November-2011): Population receptive field measurements in visual cortex of macaque monkeys, 41st Annual Meeting of the Society for Neuroscience (Neuroscience 2011), Washington, DC, USA.

Bahmani H. , Logothetis N.K. and Keliris G.A. (October-2011): Neural correlates of binocular rivalry in parietal cortex, Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting (BC11), Freiburg, Germany, Frontiers in Computational Neuroscience, 2011(Conference Abstract: BC11).

Bahmani H, Logothetis NK and Keliris G.A. (October-2011): Neural Correlates of Binocular Rivalry in Parietal Cortex, 12th Conference of Junior Neuroscientists of Tübingen (NeNA 2011), Heiligkreuztal, Germany.

Keliris G.A. , Shao Y., Papanikolaou A., Peng X., Logothetis N.K., Smirnakis S.M.: Assessing the spatio-temporal dynamics of visual receptive fields by fMRI, 40th Annual Meeting of the Society for Neuroscience (Neuroscience 2010), 40(371.6) 1.

Ecker A.S., Berens P., Keliris G.A., Bethge M., Logothetis N.K., Tolias A.S.: Decorrelated neuronal firing in cortical microcircuits, 40th Annual Meeting of the Society for Neuroscience (Neuroscience 2010), 40(73.20) 1.

Shao Y., Keliris G.A., Papanikolaou A., Fischer D.M. , Nagy D. , Jägle H , Seeliger MW , Augath M., Logothetis N.K., Smirnakis S.M.: Population receptive field mapping in a macaque monkey with macular degeneration, 40th Annual Meeting of the Society for Neuroscience (Neuroscience 2010), 40(371.7) 1.

Papanikolaou A., Keliris G.A., Peng X., Shao Y., Krapp E., Papageorgiou E., Schiefer U., Logothetis N.K.,Smirnakis S.M.: Population receptive field mapping in human subjects with visual cortical lesions, 40th Annual Meeting of the Society for Neuroscience (Neuroscience 2010), 40(371.5) 1.

Ecker A.S., Berens P., Keliris G.A., Bethge M., Logothetis N.K., Tolias A.S.: Decorrelated Firing in Cortical Microcircuits, AREADNE 2010: Research in Encoding And Decoding of Neural Ensembles, 2010 58.

Kapoor, V., K. Whittingstall, T. Panagiotaropoulos, Keliris G.A. and Logothetis, N.K.: Comparing inter-ocular switch and classical binocular rivalry in the human brain using eeg. 39th Annual Meeting of the Society for Neuroscience (Neuroscience 2009) 39(380.11), 1 (10 2009)

Keliris G.A., Tolias, A.S. and Logothetis, N.K.: Primary visual cortex contributions in perceptual supppression. 39th Annual Meeting of the Society for Neuroscience (Neuroscience 2009) 39(805.4), 1 (10 2009)

Stoewer, S., J. Duncan, Bartels, A., Keliris G.A., Logothetis, N.K. and N. Sigala: SANDBOX, an interactive fMRI data visualization toolbox. Cambridge Neuroscience Seminar for 2009 2009, 1 (03 2009)

Keliris G.A., Tolias, A.S. and Logothetis, N.K.: The Role of Primary Visual Cortex (V1) in Perceptual Suppression. FENS Abstracts 4, 220 (07 2008)

Panagiotaropoulos, T., V. Kapoor, Keliris G.A., A. Tolias and Logothetis, N.K.: Neurophysiological substrates of visual awareness in the macaque prefrontal cortex. FENS Abstracts 2008 4, 220 (07 2008)

Keliris G.A., Tolias, A.S. and Logothetis, N.K.: The Role of Primary Visual Cortex in Perceptual Awareness. AREADNE 2008: Research in Encoding and Decoding of Neural Ensembles 2, 61 (06 2008)

Panagiotaropoulos, T., V. Kapoor, Keliris G.A., A. Tolias and Logothetis, N.K.: Single units reflect visual awareness in the macaque prefrontal cortex. AREADNE 2008: Research in Encoding and Decoding of Neural Ensembles 2, 80 (06 2008)

Keliris G.A., Tolias, A.S. and Logothetis, N.K.: Binocular Flash Suppression in area V1 of the macaque. Proceedings of the iSLC 1, 1 (02 2008)

Berens, P., A. S. Ecker,Keliris G.A., Logothetis, N.K. and Tolias, A.S.: On the spatial scale of the local field potential - orientation and ocularity tuning of the local field potential in the primary visual cortex of the macaque. 37th Annual Meeting of the Society for Neuroscience (Neuroscience 2007) 37, 1 (11 2007)

Berens, P., Keliris G.A., A. S. Ecker, Logothetis, N.K. and Tolias, A.S.: Orientation tuning of the local field potential and multi-unit activity in the primary visual cortex of the macaque. 7th Göttingen Meeting of the German Neuroscience Society 7, 1 (03 2007)

Ecker, A. S., Berens, P., Keliris G.A., Logothetis, N.K. and Tolias, A.S.: A Data Management System for Electrophysiological Data Analysis. 7th Göttingen Meeting of the German Neuroscience Society 7, 1 (03 2007)

Berens, P., A. S. Ecker, A. Hoenselaar, Keliris G.A., A. G. Siapas, Logothetis, N.K. and Tolias, A.S.: Spikes are phase locked to the gamma-band of the local field potential oscillations in the primary visual cortex of the macaque. AREADNE 2006: Research in Encoding and Decoding of Neural Ensembles 1, 39 (06 2006)

Keliris G.A., Logothetis, N.K. and A. Tolias: Perceptual Suppression in area V1 of the Macaque. AREADNE 2006: Research in Encoding and Decoding of Neural Ensembles 1, 58 (06 2006)

Keliris G.A., S. M. Smirnakis, Tolias, A.S. and Logothetis, N.K.: Directional selectivity of human visual areas after adaptation to motion stimuli: an fMRI study. Society for Neuroscience‘s 35th Annual Meeting 35(619.12), 1 (11 2005)

Tolias, A. S., Keliris G.A., A. S. Ecker, A. G. Siapas, S. M. Smirnakis and Logothetis, N.K.: Structure of Interneuronal Correlations in the Primarh Visual Cortex of the Rhesus Macaque. Society for Neuroscience‘s 35th Annual Meeting 35(591.12), 1 (11 2005)

Keliris G.A., S. M. Smirnakis, Logothetis, N.K. and Tolias, A.S.: Motion processing in area V4 revealed with adaptation: Tetrode recordings in the awake behaving macaque. Society for Neuroscience‘s 34th Annual Meeting 34(301.4), 1 (2004)

Keliris G.A., S. M. Smirnakis, Z. Kourtzi, Tolias, A.S. and Logothetis, N.K.: FMRI Correlates of Perceptual Filling-in in a Moving Random Dot Paradigm. Society for Neuroscience‘s 32nd Annual Meeting 32(457.7), 1 (2002)