Emergent Computations in Trained Artificial Neural Networks and Real Brains

Synaptic plasticity allows cortical circuits to learn new tasks and to adapt to changing environments. How do cortical circuits use plasticity to acquire functions such as decision-making or working memory? Neurons are connected in complex ways, forming recurrent neural networks, and learning modifies the strength of their connections. Moreover, neurons communicate emitting brief discrete electric signals. Here we describe how to train recurrent neural networks in tasks like those used to train animals in neuroscience laboratories, and how computations emerge in the trained networks. Surprisingly, artificial networks and real brains can use similar computational strategies.Comment: International Summer School on Intelligent Signal Processing for Frontier Research and Industry, INFIERI 2021. Universidad Aut\'onoma de Madrid, Madrid, Spain. 23 August - 4 September 202

Dopamine firing plays a dual role in coding reward prediction errors and signaling motivation in a working memory task

Little is known about how dopamine (DA) neuron firing rates behave in cognitively demanding decision-making tasks. Here, we investigated midbrain DA activity in monkeys performing a discrimination task in which the animal had to use working memory (WM) to report which of two sequentially applied vibrotactile stimuli had the higher frequency. We found that perception was altered by an internal bias, likely generated by deterioration of the representation of the first frequency during the WM period. This bias greatly controlled the DA phasic response during the two stimulation periods, confirming that DA reward prediction errors reflected stimulus perception. In contrast, tonic dopamine activity during WM was not affected by the bias and did not encode the stored frequency. More interestingly, both delay-period activity and phasic responses before the second stimulus negatively correlated with reaction times of the animals after the trial start cue and thus represented motivated behavior on a trial-by-trial basis. During WM, this motivation signal underwent a ramp-like increase. At the same time, motivation positively correlated with accuracy, especially in difficult trials, probably by decreasing the effect of the bias. Overall, our results indicate that DA activity, in addition to encoding reward prediction errors, could at the same time be involved in motivation and WM. In particular, the ramping activity during the delay period suggests a possible DA role in stabilizing sustained cortical activity, hypothetically by increasing the gain communicated to prefrontal neurons in a motivation-dependent way

Integrating viral hepatitis management into the emergency department: A further step towards viral hepatitis elimination

Background & Aims: Many people with HCV and HBV infection are unaware of their condition, particularly at-risk and vulnerable populations who face barriers for screening and linkage to care. Emergency departments are often their only point of contact with the health system. Methods: This is a prospective study investigating HBsAg and HCV antibody testing, with reflex testing for HDV antibodies and HCV RNA, in adults attending an emergency department and requiring a blood test. Positive cases were linked to care. A cost-effectiveness analysis was performed. Results: From February 2020 to February 2022, a total of 17,560 individuals were screened. HBsAg was detected in 91 (0.5%), HCV RNA in 128 (0.7%), and HDV antibodies in two (0.01%) individuals. Nearly 40% of positive cases were unaware of their condition. Linkage to care was achieved in 42 of 56 HBsAg-positive and 45 of 69 HCV RNA-positive participants who were candidates for referral. HCV and HBV screening vs. no screening yielded 1.06 and 0.42 additional quality-adjusted life-years, respectively, with incremental cost–utility ratios of €7,629 and -€147 per quality-adjusted life-year gained, respectively, and proved even more cost-effective in patients with hepatitis C aged 40–70 years. Conclusions: On emergency department screening for hepatitis B, C, and D in Barcelona, the prevalence of HBsAg was 0.5% and HCV RNA 0.7%, approximately threefold higher than that observed in the general population. This strategy diagnosed patients with active HCV infection and no risk factors, who would not have been screened according to the current recommendations. Screening and linkage to care of viral hepatitis is cost-effective in this setting. Impact and implications: We evaluated the performance and cost-effectiveness of a viral hepatitis screening programme implemented in an emergency department, which aimed to identify and link to care people living with hepatitis B and C. Our findings reveal a threefold higher prevalence of hepatitis B and C than in the general Spanish population, possibly attributable to the role of the emergency department as the main healthcare gateway for vulnerable populations, who have a higher prevalence of viral hepatitis. Risk factors for viral hepatitis could not be identified in most people living with hepatitis B and C attending the emergency department; hence, screening beyond risk factors should be considered in hepatitis detection strategies. Emergency department screening is cost-effective for hepatitis C and is a cost-saving strategy for hepatitis B in our setting. These data should inform future updates to clinical guidelines