title: Associating spontaneous with evoked activity in a neural mass model of visual cortex.
abstract: Spontaneous activity of the brain at rest frequently has been considered a mere backdrop to the salient activity evoked by external stimuli or tasks. However, the resting state of the brain consumes most of its energy budget, which suggests a far more important role. An intriguing hint comes from experimental observations of spontaneous activity patterns, which closely resemble those evoked by visual stimulation with oriented gratings, except that cortex appeared to cycle between different orientation maps. Moreover, patterns similar to those evoked by the behaviorally most relevant horizontal and vertical orientations occurred more often than those corresponding to oblique angles. We hypothesize that this kind of spontaneous activity develops at least to some degree autonomously, providing a dynamical reservoir of cortical states, which are then associated with visual stimuli through learning. To test this hypothesis, we use a biologically inspired neural mass model to simulate a patch of cat visual cortex. Spontaneous transitions between orientation states were induced by modest modifications of the neural connectivity, establishing a stable heteroclinic channel. Significantly, the experimentally observed greater frequency of states representing the behaviorally important horizontal and vertical orientations emerged spontaneously from these simulations. We then applied bar-shaped inputs to the model cortex and used Hebbian learning rules to modify the corresponding synaptic strengths. After unsupervised learning, different bar inputs reliably and exclusively evoked their associated orientation state; whereas in the absence of input, the model cortex resumed its spontaneous cycling. We conclude that the experimentally observed similarities between spontaneous and evoked activity in visual cortex can be explained as the outcome of a learning process that associates external stimuli with a preexisting reservoir of autonomous neural activity states. Our findings hence demonstrate how cortical connectivity can link the maintenance of spontaneous activity in the brain mechanistically to its core cognitive functions.
authors.affiliation: Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany; Institute for Biomedical Engineering and Informatics, Technical University of Ilmenau, 98693 Ilmenau, Germany. Electronic address: nguyen@cbs.mpg.de.
authors.forename: Manh
authors.initials: M
authors.lastname: Nguyen Trong
authors.affiliation: School of Psychology (CN-CR), University of Birmingham, Edgbaston, Birmingham B15 2TT, UK; Centre for Neuroscience, Donders Institute for Brain, Cognition and Behaviour, 6500 HB Nijmegen, The Netherlands.
authors.forename: Ingo
authors.initials: I
authors.lastname: Bojak
authors.affiliation: Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Knösche
mesh_terms: D000818:Animals; D002415:Cats; D005071:Evoked Potentials / Q000502:physiology*; D007858:Learning / Q000502:physiology; D008959:Models, Neurological; D012146:Rest / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*
keywords: Learning; Neural mass; Spontaneous activity; Stable heteroclinic channels