ABSTRACT
A 57-year-old male was imaged with 123I mIBG for left sided suprarenal mass. The planar and SPECT-CT acquisitions revealed features consistent with a left sided pheochromocytoma. There was physiological and high uptake in the hypertrophied left lobe of the liver which was normal at both MRI and non-contrast CT. Asymmetrical increased 123I mIBG uptake in the left lobe of the liver as compared to the right lobe is a known physiological finding with no obvious cause or significance.
Subject(s)
3-Iodobenzylguanidine , Adrenal Gland Neoplasms , Male , Humans , Middle Aged , Tomography, X-Ray Computed , Liver/diagnostic imaging , RadiopharmaceuticalsABSTRACT
How do you make a decision if you do not know the rules of the game? Models of sensory decision-making suggest that choices are slow if evidence is weak, but they may only apply if the subject knows the task rules. Here, we asked how the learning of a new rule influences neuronal activity in the visual (area V1) and frontal cortex (area FEF) of monkeys. We devised a new icon-selection task. On each day, the monkeys saw 2 new icons (small pictures) and learned which one was relevant. We rewarded eye movements to a saccade target connected to the relevant icon with a curve. Neurons in visual and frontal cortex coded the monkey's choice, because the representation of the selected curve was enhanced. Learning delayed the neuronal selection signals and we uncovered the cause of this delay in V1, where learning to select the relevant icon caused an early suppression of surrounding image elements. These results demonstrate that the learning of a new rule causes a transition from fast and random decisions to a more considerate strategy that takes additional time and they reveal the contribution of visual and frontal cortex to the learning process.
Subject(s)
Frontal Lobe/physiology , Learning/physiology , Visual Cortex/physiology , Visual Perception/physiology , Action Potentials , Animals , Choice Behavior/physiology , Eye Movement Measurements , Haplorhini , Microelectrodes , Neurons/physiology , Reward , Saccades/physiologyABSTRACT
Stimuli associated with high rewards evoke stronger neuronal activity than stimuli associated with lower rewards in many brain regions. It is not well understood how these reward effects influence activity in sensory cortices that represent low-level stimulus features. Here, we investigated the effects of reward information in the primary visual cortex (area V1) of monkeys. We found that the reward value of a stimulus relative to the value of other stimuli is a good predictor of V1 activity. Relative value biases the competition between stimuli, just as has been shown for selective attention. The neuronal latency of this reward value effect in V1 was similar to the latency of attentional influences. Moreover, V1 neurons with a strong value effect also exhibited a strong attention effect, which implies that relative value and top-down attention engage overlapping, if not identical, neuronal selection mechanisms. Our findings demonstrate that the effects of reward value reach down to the earliest sensory processing levels of the cerebral cortex and imply that theories about the effects of reward coding and top-down attention on visual representations should be unified.
Subject(s)
Action Potentials/physiology , Attention/physiology , Reward , Visual Cortex/physiology , Analysis of Variance , Animals , Color , Cues , Haplorhini , Psychomotor Performance , Reaction Time , Saccades/physiologyABSTRACT
Visual attention can select spatial locations, features and objects. Theories of object-based attention claim that attention enhances the representation of all parts of an object, even parts that are not task relevant. We recorded neuronal activity in area V1 of macaque monkeys and observed an automatic spread of attention to image elements outside of the attentional focus when they were bound to an attended stimulus by Gestalt criteria.
