Acquiring, processing and utilising "information" is crucial to any mental function -including seemingly simple daily functions. Collectively called 'cognitive functions', these processes are a result of different regions of the brain acting together.

Disruption of these cognitive functions increases the risk of development of mental health problem. Recently it has been proposed that inflammatory pathways may contribute to disorders of cognition and behaviour like depression.

This is largely due to research showing that those with inflammatory conditions like arthritis are more likely to develop mental health problems like depression. Conversely, those who suffer from mental health problems (even in the absence of inflammatory conditions) have large amounts of inflammatory molecules in the blood. Studies in animals suggest that inflammation outside the brain can reach and affect the brain in a number of ways. So, does inflammation play a role in the development of cognitive and behavioural symptoms? What are the pathways involved?

The current project tries to address this question. Specifically, the investigators intend to use modern scanning techniques to examine the effect of inducing a low grade inflammation (using a commonly used typhoid vaccine) to see how the inflammation affects how different regions of the act together to perform cognitive functions.

Inclusion Criteria:

1. Written informed consent
2. Aged 18 - 50 years old
3. Male

Exclusion Criteria:

1. Female
2. History/family history of medical or/and Axis I DSM IV condition
3. Received typhoid vaccination within the last 3 years
4. Taken oral antibiotics/antiinflammatory agents within the previous 2 weeks
5. Current Smokers
6. Contraindication for MRI scans
7. Contraindication for Salmonella typhi vaccination
8. Known hypersensitivity to a Vi antigen containing vaccine.