Memory and Markov Blankets.

In theoretical biology, we are often interested in random dynamical systems-like the brain-that appear to model their environments. This can be formalized by appealing to the existence of a (possibly non-equilibrium) steady state, whose density preserves a conditional independence between a biological entity and its surroundings. From this perspective, the conditioning set, or Markov blanket, induces a form of vicarious synchrony between creature and world-as if one were modelling the other. However, this results in an apparent paradox. If all conditional dependencies between a system and its surroundings depend upon the blanket, how do we account for the mnemonic capacity of living systems? It might appear that any shared dependence upon past blanket states violates the independence condition, as the variables on either side of the blanket now share information not available from the current blanket state. This paper aims to resolve this paradox, and to demonstrate that conditional independence does not preclude memory. Our argument rests upon drawing a distinction between the dependencies implied by a steady state density, and the density dynamics of the system conditioned upon its configuration at a previous time. The interesting question then becomes: What determines the length of time required for a stochastic system to 'forget' its initial conditions? We explore this question for an example system, whose steady state density possesses a Markov blanket, through simple numerical analyses. We conclude with a discussion of the relevance for memory in cognitive systems like us.

A Variational Approach to Scripts.

This paper proposes a formal reconstruction of the script construct by leveraging the active inference framework, a behavioral modeling framework that casts action, perception, emotions, and attention as processes of (Bayesian or variational) inference. We propose a first principles account of the script construct that integrates its different uses in the behavioral and social sciences. We begin by reviewing the recent literature that uses the script construct. We then examine the main mathematical and computational features of active inference. Finally, we leverage the resources of active inference to offer a formal model of scripts. Our integrative model accounts for the dual nature of scripts (as internal, psychological schema used by agents to make sense of event types and as constitutive behavioral categories that make up the social order) and also for the stronger and weaker conceptions of the construct (which do and do not relate to explicit action sequences, respectively).

Repeat planar white cell scanning to monitor short-term therapy of active inflammatory bowel disease: a methodological study and comparison with clinical scores and novel inflammatory markers.

OBJECTIVES: Radiolabelled white cell scans provide non-invasive quantification of inflammatory activity. Clinical activity scores measure severity of disease but are partly subjective. White cell scans may provide a suitable method of monitoring the treatment response of active inflammatory bowel disease. METHODS: Ten subjects with active ulcerative colitis and 13 subjects with active Crohn's disease were recruited. White cell scans were carried out before and 2 weeks after treatment. Prior to each scan, activity scores for ulcerative colitis or Crohn's disease were calculated and serum and faecal tumour necrosis factor-alpha and calprotectin measured. White cell scan activity at 1 h was calculated by using a validated visual grading system. RESULTS: Following anti-inflammatory treatment, 70% of white cell scans improved, 17% remained unchanged and 13% deteriorated. In the ulcerative colitis subgroup subjects there was modest agreement for change in scan score and activity scores. In the Crohn's disease subjects there was better agreement between change of white cell scan score and clinical scores. Planar white cell scans correlated with the van Hees activity index (r=0.68, P=0.002) and faecal calprotectin (r=0.58, P=0.0003). Changes in planar white cell scans correlated with changes in serum calprotectin (r=0.45, P=0.05). CONCLUSION: Non-invasive white cell scanning is a feasible and objective method to monitor the anti-inflammatory efficacy of treatments for active inflammatory bowel disease.

Treatment of hepatitis C virus infection in intravenous drug users.

BACKGROUND: Hepatitis C virus (HCV) infection is common among intravenous drug users, and because of the long latent period, HCV liver disease is set to increase. OBJECTIVES: We sought to examine practice guidelines regarding treatment of HCV in drug users and to review the evidence for current practices. METHODS: A structured search of the Pubmed database, websites of the National Institute for Clinical Excellence and national and international expert groups and opinion of independent experts in the field. RESULTS AND CONCLUSIONS: All those infected with HCV need to be assessed to ascertain whether they have active ongoing viral replication and the extent of liver damage. HCV-infected individuals should be educated about the modes of transmission and means of reducing the risk of infecting others. They should also be advised to avoid cofactors (especially alcohol) that accelerate the progression of liver disease. Specific treatment with antivirals can cause viral clearance and prevent the progression of liver disease. Therapy is effective in those on opiate-replacement treatments and also in motivated individuals who continue to use intravenous drugs. The decision whether to treat drug users should be made jointly by specialists in the management of viral hepatitis and addiction on a case-by-case basis. Current combination drug regimens are expensive but are claimed to be cost-effective, and are certainly much less costly than managing end-stage liver disease. In addition to satisfactory sustained viral response rates, other benefits such as a beneficial effect on drug habit, self-esteem and rehabilitation have been reported. Encouraging suitable drug users to take-up and comply with treatment seems to be more easily achieved in supportive drug dependency unit settings (rather than the more formal surroundings of a hospital clinic).