Dependence of Working Memory on Coordinated Activity Across Brain Areas

Neural signatures of working memory (WM) have been reported in numerous brain areas, suggesting a distributed neural substrate for memory maintenance. In the current manuscript we provide an updated review of the literature focusing on intracranial neurophysiological recordings during WM in primates. Such signatures of WM include changes in firing rate or local oscillatory power within an area, along with measures of coordinated activity between areas based on synchronization between oscillations. In comparing the ability of various neural signatures in any brain area to predict behavioral performance, we observe that synchrony between areas is more frequently and robustly correlated with WM performance than any of the within-area neural signatures. We further review the evidence for alteration of inter-areal synchrony in brain disorders, consistent with an important role for such synchrony during behavior. Additionally, results of causal studies indicate that manipulating synchrony across areas is especially effective at influencing WM task performance. Each of these lines of research supports the critical role of inter-areal synchrony in WM. Finally, we propose a framework for interactions between prefrontal and sensory areas during WM, incorporating a range of experimental findings and offering an explanation for the observed link between intra-areal measures and WM performance.

The Rise and Fall of Dopamine: A Two-Stage Model of the Development and Entrenchment of Anorexia Nervosa

Dopamine has long been implicated as a critical neural substrate mediating anorexia nervosa (AN). Despite nearly 50 years of research, the putative direction of change in dopamine function remains unclear and no consensus on the mechanistic role of dopamine in AN has been achieved. We hypothesize two stages in AN– corresponding to initial development and entrenchment– characterized by opposite changes in dopamine. First, caloric restriction, particularly when combined with exercise, triggers an escalating spiral of increasing dopamine that facilitates the behavioral plasticity necessary to establish and reinforce weight-loss behaviors. Second, chronic self-starvation reverses this escalation to reduce or impair dopamine which, in turn, confers behavioral inflexibility and entrenchment of now established AN behaviors. This pattern of enhanced, followed by impaired dopamine might be a common path to many behavioral disorders characterized by reinforcement learning and subsequent behavioral inflexibility. If correct, our hypothesis has significant clinical and research implications for AN and other disorders, such as addiction and obesity.

NCC research and the problem of consciousness

One of the reasons why the Neural Correlates of Consciousness Program could appear attractive in the 1990s was that it seemed to disentangle theoretical and empirical problems. Theoretical disagreements could thus be sidestepped in order to focus on empirical research regarding the neural substrate of consciousness. One of the further consequences of this dissociation of empirical and theoretical questions was that fundamental questions regarding the Mind Body Problem or the “Hard Problem of Consciousness” could remain unresolved even if the search for the neural correlates had been successful.Drawing on historical examples, a widely held consensus in the philosophy of science, and actual NCC research we argue that there is no such independence. Moreover, as the dependence between the theoretical and the empirical level is mutual, empirical progress will go hand in hand with theoretical development. Thus, contrary to what the original NCC program suggested, we conclude that NCC research may significantly take advantage from and contribute to theoretical progress in our explanation and understanding of consciousness. Eventually, this might even contribute to a solution of the Hard Problem of Consciousness.

Adaptive neurons compute confidence in a decision network

Humans and many animals have the ability to assess the confidence of their decisions. However, little is known about the underlying neural substrate and mechanism. In this study we propose a computational model consisting of a group of ’confidence neurons’ with adaptation, which are able to assess the confidence of decisions by detecting the slope of ramping activities of decision neurons. The simulated activities of ’confidence neurons’ in our simple model capture the typical features of confidence observed in humans and animals experiments. Our results indicate that confidence could be online formed along with the decision formation, and the adaptation properties could be used to monitor the formation of confidence during the decision making.

A neural substrate for Bayesian integration in human parietal cortex

Making adaptive decisions often requires inferring unobservable states based on unreliable information. Bayesian logic prescribes that individuals form probabilistic beliefs about a state by integrating the likelihood of new evidence with their prior beliefs, but human neuroimaging studies on probability representations have not typically examined this integration process. We developed an inference fMRI task in which participants estimated the posterior probability of a hidden state while we parametrically modulated the prior probability of the state, the likelihood of the supporting evidence, and a monetary penalty for estimation inaccuracy. Consistent with a neural substrate for Bayesian integration, activation in left posterior parietal cortex tracked the estimated posterior probability of the solicited state and its components of prior probability and likelihood, all independently of expected value. This activation further reflected deviations in individual reports from objective probabilities. Thus, this region may provide a neural substrate for humans' ability to approximate Bayesian inference.

The Interstitial Pathways as the Substrate of Consciousness: A New Synthesis

This paper considers three classes of analyses of the nature of consciousness: abstract theories of the functional organization of consciousness, and concrete proposals as to the neural substrate of consciousness, while providing a rationale for contesting non-neural and transcendental conceptualizations of consciousness. It indicates that abstract theories of the dynamic core of consciousness have no force unless they are grounded in the physiology of the brain, since the organization of dynamic systems, such as the Sun, could equally well qualify as conscious under such theories. In reviewing the wealth of studies of human consciousness since the mid-20th century, it concludes that many proposals for the particular neural substrate of consciousness are insufficient in various respects, but that the results can be integrated into a novel scheme that consciousness extends through a subcortical network of interlaminar structures from the brainstem to the claustrum. This interstitial structure has both the specificity and the extended connectivity to account for the array of reportable conscious experiences.