Faculty Bibliography

Optimal choices benefit from previous learning. However, it is not clear how previously learned stimuli influence behavior to novel but similar stimuli. One possibility is to generalize based on the similarity between learned and current stimuli. Here, we use neuroscientific methods and a novel computational model to inform the question of how stimulus generalization is implemented in the human brain. Behavioral responses during an intradimensional discrimination task showed similarity-dependent generalization. Moreover, a peak shift occurred, i.e., the peak of the behavioral generalization gradient was displaced from the rewarded conditioned stimulus in the direction away from the unrewarded conditioned stimulus. To account for the behavioral responses, we designed a similarity-based reinforcement learning model wherein prediction errors generalize across similar stimuli and update their value. We show that this model predicts a similarity-dependent neural generalization gradient in the striatum as well as changes in responding during extinction. Moreover, across subjects, the width of generalization was negatively correlated with functional connectivity between the striatum and the hippocampus. This result suggests that hippocampus-striatal connections contribute to stimulus-specific value updating by controlling the width of generalization. In summary, our results shed light onto the neurobiology of a fundamental, similarity-dependent learning principle that allows learning the value of stimuli that have never been encountered.

Rewards in the natural environment are rarely predicted with complete certainty. Uncertainty relating to future rewards has typically been defined as the variance of the potential outcomes. However, the asymmetry of predicted reward distributions, known as skewness, constitutes a distinct but neuroscientifically underexplored risk term that may also have an impact on preference. By changing only reward magnitudes, we study skewness processing in equiprobable ternary lotteries involving only gains and constant probabilities, thus excluding probability distortion or loss aversion as mechanisms for skewness preference formation. We show that individual preferences are sensitive to not only the mean and variance but also to the skewness of predicted reward distributions. Using neuroimaging, we show that the insula, a structure previously implicated in the processing of reward-related uncertainty, responds to the skewness of predicted reward distributions. Some insula responses increased in a monotonic fashion with skewness (irrespective of individual skewness preferences), whereas others were similarly elevated to both negative and positive as opposed to no reward skew. These data support the notion that the asymmetry of reward distributions is processed in the brain and, taken together with replicated findings of mean coding in the striatum and variance coding in the cingulate, suggest that the brain codes distinct aspects of reward distributions in a distributed fashion.

OBJECTIVES: This retrospective study aimed to evaluate the diagnostic utility of ultrasound-guided core biopsy (USCB) in lymphoma of the head and neck, in particular whether core biopsy can provide sufficient diagnostic information for definitive treatment. METHODS: All lymphomas diagnosed in the head and neck at Eastbourne General Hospital between January 2000 and June 2009 were identified. Radiology and pathology reports were reviewed and the diagnostic techniques recorded. The type of biopsy (fine needle aspiration, needle core, surgical excision biopsy) used to establish a diagnosis sufficient to allow treatment, i.e. the "index" diagnostic technique, was identified. Previous inconclusive or inadequate biopsies were noted. Pathology reports based on USCB were graded 0-3 according to diagnostic completeness and ability to provide treatment information. RESULTS: Of 691 overall cases of lymphoma diagnosed over the 9 year period, 171 different patients presented with lymphoma in the head and neck. Of these 171, 83 had USCB biopsy during diagnostic work up. 60 were regarded as grade 3 where a confident diagnosis of lymphoma was made. In seven patients, clinical management proceeded on the basis of a suggestive (grade 2) pathology report without surgical excision, and these were therefore also included as "index" biopsies. Overall therefore, 67/83 core biopsies (81%) provided adequate information to allow treatment. Surgical excision biopsy was the index modality in 104 cases. CONCLUSION: In the majority of cases USCB is adequate for confident histopathological diagnosis avoiding the need for surgical excision biopsy in cases of suspected head and neck lymphoma.

Professionalism is a complex blend of values, behaviours, ideals and obligations that are hard to define but recognizable when observed. This article reflects on medical professionalism as an entity, reviews the challenges it faces, and considers proactive ways of nurturing the concept of professionalism in radiology.

Advances in imaging have led to improved sensitivity in the diagnosis of diseases that involve the major salivary glands. Ultrasound (US), plain radiography and sialography, magnetic resonance imaging (MRI), computed tomography (CT), and nuclear scintigraphy/positron emission tomography (PET) all play a part, and imaging often assists in the planning of further management, operative or otherwise. We review the methods used for imaging the major salivary glands, and apply the indications for these methods to the principal pathological processes.

BACKGROUND: Multidetector computed tomography (MDCT) has become the main investigation of choice for staging of many cancers. AIM: The purpose of this pictorial review is to discuss the imaging appearances on CT of some of the more common cancers arising within the abdomen and pelvis and to describe their typical sites of local, nodal and haematogenous tumour spread. METHODS: Cancers arising from the stomach, pancreas, colon, kidney, ovary and prostate will be reviewed. RESULTS: Awareness of the characteristic sites of tumour spread is important to allow accurate identification of all sites of disease. CONCLUSION: This will clearly have an impact on both patient management and prognosis.