Frontopolar signaling of inferred value

Adaptive decision-making requires that options be weighed according to the predicted value of the outcomes that they are likely to produce. Cognitive neuroscientific research has frequently emphasized the importance of the ventromedial prefrontal cortex (VMPFC) for encoding value information. As measured via functional MRI, VMPFC activity has been shown to correlate with the subjective values of explicitly-presented options (e.g., monetary gambles, offered foods) and also with the learned values of stimuli or actions that have been arbitrarily paired with rewards or punishments. Additional work has confirmed VMPFC sensitivity to abrupt changes in option values, particularly when these may be inferred on the basis of regular fluctuations in and/or interrelationships between option-outcome contingencies (e.g., as in serial reversal learning). The use of fixed option alternatives in these settings (e.g., constant choice stimuli) raises the question of whether such rapid updating of value activity can only occur when inferences can rely upon concretely-encoded sensory and motor information. To determine whether any brain region tracks values that may only be inferred via abstract rules, we scanned 17 participants as they completed a series of unique, two-trial discrimination problems in which the stimulus chosen on each Trial 1 was replaced with a novel stimulus of the same reward status on the following Trial 2. Under this protocol, optimal responding required inferences regarding the valence of each unsampled Trial 1 stimulus. Additional problem-wise manipulation of the magnitude of the available gains and losses created a situation in which the specific values of the unsampled stimuli could also be inferred. BOLD-signal analyses revealed activity in the right lateral frontopolar cortex (FPC) that varied linearly with the inferable values of the unsampled Trial 1 stimuli; follow-up analyses confirmed that this effect was not attributable to the influence of the recently-delivered Trial 1 outcomes. Therefore, the results indicate that the brain does encode values that may only be inferred via abstract deduction. The frontopolar focus of this inferred-value activity corroborates and expands upon recent accounts of FPC function, which posit a broader role for this region in monitoring the value of re-directing behavior towards postponed response options

Investigating the function of the ventral visual reading pathway and its involvement in acquired reading disorders

This thesis investigated the role of the left ventral occipitotemporal (vOT) cortex and how damage to this area causes peripheral reading disorders. Functional magnetic resonance imaging (fMRI) studies in volunteers demonstrated that the left vOT is activated by written words over numbers or perceptually-matched baselines, irrespective of the word’s location on the visual field. Mixed results were observed for the comparison of words versus false font stimuli. This response profile suggests that the left vOT is preferentially activated by words or word-like stimuli, due to either: (1) bottom-up specialisation for processing familiar word-forms; (2) top-down task-dependent modulation, or (3) a combination of the two. Further studies are proposed to discriminate between these possibilities. Thirteen patients with left occipitotemporal damage participated in the rehabilitation and fMRI studies. The patients were impaired on word, text and letter reading. A structural analysis showed that damage to the left occipitotemporal white matter, in the vicinity of the inferior longitudinal fasciculus, was associated with slow word reading speed. The fMRI study showed that the patients had reduced activation of the bilateral posterior superior temporal sulci relative to controls. Activity in this area correlated with reading speed. The efficacy of intensive whole-word recognition training was tested. Immediately after the training, trained words were read faster than untrained words, but the effects did not persist until the follow-up assessment. Hence, damage to the left vOT white matter impairs rapid whole-word recognition and is resistant to rehabilitation. The final study investigated the role of spatial frequency (SF) in the lateralisation of vOT function. Lateralisation of high and low SF processing was demonstrated, concordant with the lateralisation for words and faces to the left and right vOT respectively. A perceptual basis for the organisation of vOT cortex might explain why left vOT damage is resistant to treatment

The modularity of aesthetic processing and perception in the human brain. Functional neuroimaging studies of neuroaesthetics.

By taking advantage of the advent of functional Magnetic Resonance Imaging (fMRI) this thesis argues that aesthetics belongs in the domain of neurobiology by investigating the different brain processes that are implicated in aesthetic perception from two perspectives. The first experiment explores a specific artistic style that has stressed the problem in the relationship between objects and context. This study investigates the neural responses associated with changes in visual perception, as when objects are placed in their normal context versus when the object-context relationship is violated. Indeed, an aim of this study was to cast a new light on this specific artistic style from a neuroscientific perspective. In contrast to basic rewards, which relate to the reproduction of the species, the evolution of abstract, cognitive representations facilitates the use of a different class of rewards related to hedonics. The second part investigates the hedonic processes involved in aesthetic judgments in order to explore if such higher order cognitive rewards use the same neural reward mechanism as basic rewards. In the first of these experiments we modulate the extent to which the neural correlates of aesthetic preference vary as a function of expertise in architecture. In the second experiment we aim to measure the more general effects of labelling works of art with cognitive semantic information in order to explore the neural modulation of aesthetic preference relative to this information. The main finding of this thesis is that stimulus affective value is represented separately in OFC, with positive reward (increasing aesthetic judgments) being represented in medial OFC and negative reward value is being represented in lateral OFC. Furthermore ventral striatum encode reward expectancy and the predictive value of a stimulus. These findings suggest a dissociation of reward processing with separate neural substrates in reward expectancy and stimulus affective value

Low-frequency oscillatory correlates of auditory predictive processing in cortical-subcortical networks: a MEG-study

Emerging evidence supports the role of neural oscillations as a mechanism for predictive information processing across large-scale networks. However, the oscillatory signatures underlying auditory mismatch detection and information flow between brain regions remain unclear. To address this issue, we examined the contribution of oscillatory activity at theta/alpha-bands (4–8/8–13 Hz) and assessed directed connectivity in magnetoencephalographic data while 17 human participants were presented with sound sequences containing predictable repetitions and order manipulations that elicited prediction-error responses. We characterized the spectro-temporal properties of neural generators using a minimum-norm approach and assessed directed connectivity using Granger Causality analysis. Mismatching sequences elicited increased theta power and phase-locking in auditory, hippocampal and prefrontal cortices, suggesting that theta-band oscillations underlie prediction-error generation in cortical-subcortical networks. Furthermore, enhanced feedforward theta/alpha-band connectivity was observed in auditory-prefrontal networks during mismatching sequences, while increased feedback connectivity in the alpha-band was observed between hippocampus and auditory regions during predictable sounds. Our findings highlight the involvement of hippocampal theta/alpha-band oscillations towards auditory prediction-error generation and suggest a spectral dissociation between inter-areal feedforward vs. feedback signalling, thus providing novel insights into the oscillatory mechanisms underlying auditory predictive processing

Impairment of Auditory-Motor Timing and Compensatory Reorganization after Ventral Premotor Cortex Stimulation

Integrating auditory and motor information often requires precise timing as in speech and music. In humans, the position of the ventral premotor cortex (PMv) in the dorsal auditory stream renders this area a node for auditory-motor integration. Yet, it remains unknown whether the PMv is critical for auditory-motor timing and which activity increases help to preserve task performance following its disruption. 16 healthy volunteers participated in two sessions with fMRI measured at baseline and following rTMS (rTMS) of either the left PMv or a control region. Subjects synchronized left or right finger tapping to sub-second beat rates of auditory rhythms in the experimental task, and produced self-paced tapping during spectrally matched auditory stimuli in the control task. Left PMv rTMS impaired auditory-motor synchronization accuracy in the first sub-block following stimulation (p<0.01, Bonferroni corrected), but spared motor timing and attention to task. Task-related activity increased in the homologue right PMv, but did not predict the behavioral effect of rTMS. In contrast, anterior midline cerebellum revealed most pronounced activity increase in less impaired subjects. The present findings suggest a critical role of the left PMv in feed-forward computations enabling accurate auditory-motor timing, which can be compensated by activity modulations in the cerebellum, but not in the homologue region contralateral to stimulation

Real-time decoding of question-and-answer speech dialogue using human cortical activity.

Natural communication often occurs in dialogue, differentially engaging auditory and sensorimotor brain regions during listening and speaking. However, previous attempts to decode speech directly from the human brain typically consider listening or speaking tasks in isolation. Here, human participants listened to questions and responded aloud with answers while we used high-density electrocorticography (ECoG) recordings to detect when they heard or said an utterance and to then decode the utterance's identity. Because certain answers were only plausible responses to certain questions, we could dynamically update the prior probabilities of each answer using the decoded question likelihoods as context. We decode produced and perceived utterances with accuracy rates as high as 61% and 76%, respectively (chance is 7% and 20%). Contextual integration of decoded question likelihoods significantly improves answer decoding. These results demonstrate real-time decoding of speech in an interactive, conversational setting, which has important implications for patients who are unable to communicate