Daniel Durstewitz

The computational role of dopamine D1 receptors in working memory

The prefrontal cortex (PFC) is essential for working memory, which is the ability to transiently hold and manipulate information necessary for generating forthcoming action. PFC neurons actively encode working memory information via sustained firing patterns. Dopamine via D1 receptors potently modulates sustained activity of PFC neurons and performance in working memory tasks. In vitro patch-clamp data have revealed many different cellular actions of dopamine on PFC neurons and synapses. These effects were simulated using realistic networks of recurrently connected assemblies of PFC neurons. Simulated D1-mediated modulation led to a deepening and widening of the basins of attraction of high (working memory) activity states of the network, while at the same time background activity was depressed. As a result, self-sustained activity was more robust to distracting stimuli and noise. In this manner, D1 receptor stimulation might regulate the extent to which PFC network activity is focused on a particular goal state versus being open to new goals or information unrelated to the current goal.

The dopaminergic innervation of the avian telencephalon

The present review provides an overview of the distribution of dopaminergic fibers and dopaminoceptive elements within the avian telencephalon, the possible interactions of dopamine (DA) with other biochemically identified systems as revealed by immunocytochemistry, and the involvement of DA in behavioral processes in birds. Primary sensory structures are largely devoid of dopaminergic fibers, DA receptors and the D1-related phosphoprotein DARPP-32, while all these dopaminergic markers gradually increase in density from the secondary sensory to the multimodal association and the limbic and motor output areas. Structures of the avian basal ganglia are most densely innervated but, in contrast to mammals, show a higher D2 than D1 receptor density. In most of the remaining telencephalon D1 receptors clearly outnumber D2 receptors. Dopaminergic fibers in the avian telencephalon often show a peculiar arrangement where fibers coil around the somata and proximal dendrites of neurons like baskets, probably providing them with a massive dopaminergic input. Basket-like innervation of DARPP-32-positive neurons seems to be most prominent in the multimodal association areas. Taken together, these anatomical findings indicate a specific role of DA in higher order learning and sensory-motor processes, while primary sensory processes are less affected. This conclusion is supported by behavioral findings which show that in birds, as in mammals, DA is specifically involved in sensory-motor integration, attention and arousal, learning and working memory. Thus, despite considerable differences in the anatomical organization of the avian and mammalian forebrain, the organization of the dopaminergic system and its behavioral functions are very similar in birds and mammals.

Neural representation of interval time.

Animals can predict the time of occurrence of a forthcoming event relative to a preceding stimulus, i.e. the interval time between those two, given previous learning experience with the temporal contingency between them. Accumulating evidence suggests that a particular pattern of neural activity observed during tasks involving fixed temporal intervals might carry interval time information: the activity of some cortical and subcortical neurons ramps up slowly and linearly during the interval, like a temporal integrator, and peaks around the time at which the event is due to occur. The slope of this climbing activity, and hence the peak time, adjusts to the length of a temporal interval during repetitive experience with it. Various neural mechanisms for producing climbing activity with variable slopes, representing the length of learned intervals, are discussed.

Phänomenales Erleben: Ein fundamentales Problem für die Psychologie und die Neurowissenschaften

Zusammenfassung. In diesem Artikel versuchen wir aufzuzeigen, in welchem speziellen Sinne Bewustsein ein Problem darstellt, fur das die Psychologie und die Neurowissenschaften derzeit keinerlei theoretische Erklarung und kein methodisches Konzept haben. In experimentellen Arbeiten wird Bewustsein meist verstanden als ein aufmerksamkeitsgekoppelter Zustand oder Prozes, der selbst-referentielle Metakognitionen und darauf aufbauende kognitive Operationen ermoglicht. Diese Konzeption reduziert Bewustsein auf vergleichsweise “einfache” Probleme, die mit den bekannten naturwissenschaftlichen Ansatzen gelost werden konnen. Sie last aber unserer Meinung nach einen wesentlichen, viel schwierigeren Aspekt auser acht: Die Frage nach der Entstehung und der Funktion des phanomenalen Erlebens, der “Qualia”. Wir zeigen auf, das dieses Problem zur Zeit prinzipiell unlosbar erscheint und argumentieren, das sich darin eine fundamentale Wissenslucke der Psychologie und der gesamten Naturwissenschaften widerspiegelt, die ern...

The Possible Function of Dopamine in Associative Learning: A Computational Model

The neuromodulator dopamine is critically involved in different procedures of instrumental learning and working memory. Based on physiological data, the present study investigates the effects of dopamine on neural network behavior. We demonstrate that dopamine suppresses interference with previously learned patterns and may enable fast learning of new contingencies or associations in biologically significant contexts.

The Principle of Species Independent Learning Phenomena

Learning theory provides an exceptionally successful framework to predict the behavior of humans and other animals in learning situations. Unfortunately research has concentrated mostly on the small number of conditions in which learning theory fails without devoting similar efforts to explain why predictions are successful in the vast majority of the remaining cases. Here, we will outline that the success of learning research is possibly related to the fact that learning implies modifications of synapses contingent on the temporal order of spikes. Spiking-time-dependent synaptic modifications reflect the temporal asymmetry of the physical world, a fundamental constraint common to all living beings which might have shaped the molecular architecture from very early on. Resource limitations might have led to additional constraints, producing deviations from general learning theory. As one example, we will discuss the apparent inability of pigeons to associate tones with visual cues. This case illustrates nicely that the specific constraints in pigeons are very likely related to an absence of a common synaptic territory of the auditory and the visual system in higher association areas. Hence, additional constraints might involve local architectural specializations of neural systems without corroborating the general framework of learning theory.