219 research outputs found
Direct and indirect communication between functionally different regions of the rat striatum
Full text linkGroenewegen, H.J. [Promotor]Pennartz, C.M.A. [Promotor
Episodic memory and the role of the brain's default-mode network
Full text linkItem does not contain fulltextThis thesis provides a number of new insights into episodic memory and the role of the default-mode network. First, it provides the first direct evidence for the contrasting role of DMN during encoding and retrieval. Secondly, the experimental findings eliminate several possible explanations for the role of the DMN, including a simple reallocation account and the orienting of attention account. Moreover, the present work sheds light on the contribution of different processes - including respiratory - to the fMRI signal. Finally, the work clarifies the flexible nature of the DMN, for example, the distinct role of the hippocampus during encoding. Overall, the work within this thesis clearly indicates that the individual DMN regions provide distinct contributions to learning and remembering.Universiteit van Amsterdam, 17 december 2010Promotor : Pennartz, C.M.A. Co-promotor : Daselaar, S.M.139 p
The brain’s representational power:on consciousness and the integration of modalities
No full textAlthough science has made considerable progress in discovering the neural basis of cognitive processes, how consciousness arises remains elusive. In this book, Cyriel Pennartz analyzes which aspects of conscious experience can be peeled away to access its core: the "hardest" aspect, the relationship between brain processes and the subjective, qualitative nature of consciousness. Pennartz traces the problem back to its historical roots in the foundations of neuroscience and connects early ideas on sensory processing to contemporary computational neuroscience.What can we learn from neural network models, and where do they fall short in bridging the gap between neural processes and conscious experience? Do neural models of cognition resemble inanimate systems, and how can this help us define requirements for conscious processing in the brain? These questions underlie Pennartz’s examination of the brain’s anatomy and neurophysiology. The perspective of his account is not limited to visual perception but broadened to include other sensory modalities and their integration. Formulating a representational theory of the neural basis of consciousness, Pennartz outlines properties that complex structures must express to process information consciously. This theoretical framework is constructed using empirical findings from neuropsychology and neuroscience as well as such theoretical arguments as the Cuneiform Room and the Wall Street Banker. Positing that qualitative experience is a multimodal and multilevel phenomenon at its very roots, Pennartz places this body of theory in the wider context of mind-brain philosophy, examining implications for our thinking about animal and robot consciousness
Cellular mechanisms underlying spontaneous firing rat suprachiasmatic nucleus: involvement of a slowly inactivating component of sodium current.
Full text link Pennartz, C.M.A., M. A. Bierlaagh, and A.M.S. Geurtsen. Cellular mechanisms underlying spontaneous firing in rat suprachiasmatic nucleus: involvement of a slowly inactivating component of sodium current. J. Neurophysiol. 78: 1811–1825, 1997. Neurons constituting the pacemaker of circadian rhythms, located in the suprachiasmatic nucleus, generate spontaneous firing patterns that change across the day-night cycle. Their average spontaneous firing rate is considered an important functional marker of clock activity because it is highest during daytime and low at night. In this study we investigate the ionic mechanisms underlying spontaneous firing in acutely prepared slices and dissociated neurons of the suprachiasmatic nucleus. In current-clamp mode, spontaneous action potentials were consistently preceded by depolarizing ramps. These ramps were Na+ dependent, were sensitive to tetrodotoxin (TTX), and disappeared on hyperpolarization. Ramps and associated spikes were not abolished by blockers of the H current (1 mM cesium) or calcium currents (50 μM nickel or 200 μM cadmium). In voltage-clamped neurons in slices or dissociated neurons, TTX-sensitive and Na+-dependent inward current was observed to activate well below firing threshold (−60 to −50 mV). The low-threshold component of Na+ current inactivated slowly as compared with the fast component that mediates action potentials. However, its inactivation proceeded more rapidly than has been reported for the persistent Na+ current in cortical structures. Persistent Na+ current was generally absent or small in amplitude. The voltage dependence and kinetics of the slowly inactivating component of Na+ current are consistent with the hypothesis that it is partially deinactivated during spike afterhyperpolarizations and contributes significantly to subsequent depolarizing ramps. These observations implicate the slowly inactivating component of Na+ current in ionic mechanisms governing spontaneous firing in suprachiasmatic nucleus neurons. </jats:p
Plasticity of neuronal firing in deep layers of the medial prefrontal cortex in rats engaged in operant conditioning.
No full textWhat is neurorepresentationalism?:From neural activity and predictive processing to multi-level representations and consciousness
Full text linkThis review provides an update on Neurorepresentationalism, a theoretical framework that defines conscious experience as multimodal, situational survey and explains its neural basis from brain systems constructing best-guess representations of sensations originating in our environment and body (Pennartz, 2015). It posits that conscious experience is characterized by five essential hallmarks: (i) multimodal richness, (ii) situatedness and immersion, (iii) unity and integration, (iv) dynamics and stability, and (v) intentionality. Consciousness is furthermore proposed to have a biological function, framed by the contrast between reflexes and habits (not requiring consciousness) versus goal-directed, planned behavior (requiring multimodal, situational survey). Conscious experience is therefore understood as a sensorily rich, spatially encompassing representation of body and environment, while we nevertheless have the impression of experiencing external reality directly. Contributions to understanding neural mechanisms underlying consciousness are derived from models for predictive processing, which are trained in an unsupervised manner, do not necessarily require overt action, and have been extended to deep neural networks. Even with predictive processing in place, however, the question remains why this type of neural network activity would give rise to phenomenal experience. Here, I propose to tackle the Hard Problem with the concept of multi-level representations which emergently give rise to multimodal, spatially wide superinferences corresponding to phenomenal experiences. Finally, Neurorepresentationalism is compared to other neural theories of consciousness, and its implications for defining indicators of consciousness in animals, artificial intelligence devices and immobile or unresponsive patients with disorders of consciousness are discussed
Electrophysiology of the rat nucleus accumbens : local circuitry, neuromodulation and synaptic plasticity
No full textIdentification and integration of sensory modalities: Neural basis and relation to consciousness
No full textA key question in studying consciousness is how neural operations in the brain can identify streams of sensory input as belonging to distinct modalities, which contributes to the representation of qualitatively different experiences. The basis for identification of modalities is proposed to be constituted by self-organized comparative operations across a network of unimodal and multimodal sensory areas. However, such network interactions alone cannot answer the question how sensory feature detectors collectively account for an integrated, yet phenomenally differentiated experiential content. This problem turns out to be different from, although related to, the binding problem. It is proposed that the neural correlate of an enriched, multimodal experience is constituted by the attractor state of a dynamic associative network. Within this network, unimodal and multimodal sensory maps continuously interact to influence each other's attractor state, so that a feature change in one modality results in a fast re-coding of feature information in another modality. In this scheme, feature detection is coded by firing-rate, whereas firing phase codes relational aspects
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