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A comprehensive understanding of how the brain responds to a changing environment requires techniques capable of recording functional outputs at the whole-brain level in response to external stimuli. Positron emission tomography (PET) is an exquisitely sensitive technique for imaging brain function but the need for anaesthesia to avoid motion artefacts precludes concurrent behavioural response studies. Here, we report a technique that combines motion-compensated PET with a robotically-controlled animal enclosure to enable simultaneous brain imaging and behavioural recordings in unrestrained small animals. The technique was used to measure in vivo displacement of [11C]raclopride from dopamine D2 receptors (D2R) concurrently with changes in the behaviour of awake, freely moving rats following administration of unlabelled raclopride or amphetamine. The timing and magnitude of [11C]raclopride displacement from D2R were reliably estimated and, in the case of amphetamine, these changes coincided with a marked increase in stereotyped behaviours and hyper-locomotion. The technique, therefore, allows simultaneous measurement of changes in brain function and behavioural responses to external stimuli in conscious unrestrained animals, giving rise to important applications in behavioural neuroscience.

Studying the neurobiology of language has begun to shift away from investigating individual regions in the brain to understanding how interactions among these regions bring about language functions. Here, we review common multivariate analysis techniques for neuroimaging data that have been used to investigate the brain networks underlying reading. For each technique, we describe the method as well as its advantages compared to other methods. We then provide examples showing how the technique has been used to understand better the functional neural architecture supporting reading.

Microglia are rapidly activated by a wide range of neuropathological insults. Quantifying microglial density in vivo would allow a new, potentially important range of clinic-pathological correlations. Microglia express the 18kDa translocator protein (TSPO) which can be quantified by the positron emission tomography (PET) ligand [(11)C]PK11195, although signal quantification is limited by nonspecific binding. New generation TSPO radioligands with an improved signal-to-noise ratio are now available, but variation in their binding affinity for the TSPO between subjects complicates their use. This review describes the principles of PET imaging, the rationale and challenges in targeting the TSPO as means of quantifying microglial activation in vivo, and disease applications that have been studied with TSPO-PET hitherto.

This chapter describes the basic principles of positron emission tomography (PET), discusses the production and characteristics of commonly employed PET tracers and probes, examines the design and performance of modern PET scanners, and discusses the process of image reconstruction and the use of tracer kinetic models to turn a time sequence of PET images into quantitative regional biological assays. PET—a powerful noninvasive imaging tool—embodies the modern concept of biological imaging, bringing together the highly specific assays of the biological sciences with sophisticated imaging technology. PET images can be fully quantitative, such that there is a linear relationship between the concentration of the labeled imaging probe and the count density measured in the PET images. The absolute concentration can then be determined by cross calibration to a known source. In order to make PET images fully quantitative, a number of correction procedures must be carefully applied. The largest of the correction factors is that required to correct for gamma-ray attenuation by the tissue. An important aspect of PET is the ability to monitor the spatial distribution of the imaging probe or tracer as a function of time. The rate of accumulation or clearance of the probe contains information about the rate of the biological processes or the characteristics of the molecular target involved. Advances in PET instrumentation and technology continue at a remarkable pace and have brought about an order of magnitude improvement in the resolving power and sensitivity of PET scanners over the past several years, resulting in a significantly clearer picture of the brain.