Excessive body fat linked to blunted somatosensory cortex response to general reward in adolescents.

BACKGROUND AND AIMS: The brain reward system is key to understanding adolescent obesity in the current obesogenic environment, rich in highly appetising stimuli, to which adolescents are particularly sensitive. We aimed to examine the association between body fat levels and brain reward system responsivity to general (monetary) rewards in male and female adolescents. METHODS: Sixty-eight adolescents (34 females; mean age (s.d.)= 16.56 (1.35)) were measured for body fat levels with bioelectric impedance, and underwent a functional magnetic resonance imaging (fMRI) scan during the Monetary Incentive Delay (MID) task. The MID task reliably elicits brain activations associated with two fundamental aspects of reward processing: anticipation and feedback. We conducted regression analyses to examine the association between body fat and brain reward system responsivity during reward anticipation and feedback, while controlling for sex, age and socioeconomic status. We also analysed the moderating impact of sex on the relationship between fat levels and brain responsivity measures. Brain imaging analyses were corrected for multiple comparisons, with a cluster-defining threshold of P<0.001, and minimum cluster size of 38 contiguous voxels. RESULTS: Higher body fat levels were associated with lower activation of the primary somatosensory cortex (S1) and the supramarginal gyrus during reward feedback after controlling for key sociodemographic variables. Although we did not find significant associations between body fat and brain activations during reward anticipation, S1/supramarginal gyrus activation during feedback was linked to increased negative prediction error, that is, less reward than expected, in illustrative post hoc analyses. Sex did not significantly moderate the association between body fat and brain activation in the MID task. CONCLUSIONS: In adolescents, higher adiposity is linked to hypo-responsivity of somatosensory regions during general (monetary) reward feedback. Findings suggest that adolescents with excess weight have blunted activation in somatosensory regions involved in reward feedback learning.

Monetary reward magnitude effects on behavior and brain function during goal-directed behavior.

Reward may modulate the cognitive processes required for goal achievement, while individual differences in personality may affect reward modulation. Our aim was to test how different monetary reward magnitudes modulate brain activation and performance during goal-directed behavior, and whether individual differences in reward sensitivity affect this modulation. For this purpose, we scanned 37 subjects with a parametric design in which we varied the magnitude of monetary rewards (€0, €0.01, €0.5, €1 or €1.5) in a blocked fashion while participants performed an interference counting-Stroop condition. The results showed that the brain activity of left dorsolateral prefrontal cortex (DLPFC) and the striatum were modulated by increasing and decreasing reward magnitudes, respectively. Behavioral performance improved as the magnitude of monetary reward increased while comparing the non reward (€0) condition to any other reward condition, or the lower €0.01 to any other reward condition, and this improvement was related with individual differences in reward sensitivity. In conclusion, the locus of influence of monetary incentives overlaps the activity of the regions commonly involved in cognitive control.

A new window to understanding individual differences in reward sensitivity from attentional networks.

Existing evidence suggests that the presence of reward cues modifies the activity in attentional networks, however, the nature of these influences remains poorly understood. Here, we performed independent component analysis (ICA) in two fMRI datasets corresponding to two incentive delay tasks, which compared the response to reward (money and erotic pictures) and neutral cues, and yielded activations in the ventral striatum using a general linear model approach. Across both experiments, ICA revealed that both the right frontoparietal network and default mode network time courses were positively and negatively modulated by reward cues, respectively. Moreover, this dual neural response pattern was enhanced in individuals with strong reward sensitivity. Therefore, ICA may be a complementary tool to investigate the relevant role of attentional networks on reward processing, and to investigate reward sensitivity in normal and pathological populations.

A cognitive neuroscience approach to individual differences in sensitivity to reward.

The Reinforcement Sensitivity Theory proposes that a neurobiological system, the Behavioral Activation System, defines individual differences on the subject's sensitivity and reactivity to appetitive stimuli associated with mesocorticolimbic structures, while this system does not mediate aversive stimulus processing. However, Jeffrey A. Gray's model also predicts the system's antagonism between this appetitive system and another aversive stimulus sensitive system, the Behavioral Inhibitory System/Fight-Flight-Freeze System, mostly associated with limbic structures. Therefore, direct modulation of brain activation during appetitive stimulus processing should be expected from the Behavioral Activation System, while inverse modulation during aversive stimulus processing may be expected to reflect the system's antagonism. Using the Sensitivity to Reward scale of the SPSR questionnaire to assess individual differences in the activity of the reward system, we present different behavioral and neuroimaging data to illustrate our view. The first experiment was based on a simple letter-judgment task while viewing erotic and aversive pictures selected from the International Affective Picture System. A second experiment employed a task performed by participants to detect infrequent aversive (i.e., stop) signals when responding to reward. The results from these studies were consistent with the idea that Behavioral Activation System-related personality traits mediate the brain activation associated with appetitive stimulus processing in reward-related areas, while it also showed its antagonism to aversive systems through a negative mediation on the limbic cortex activation. To conclude, sensitivity to reward may be understood as a form of impulsivity related to both better appetitive learning and poorer aversive learning.

Striatum gray matter reduction in males with an overactive behavioral activation system.

Using optimized voxel-based morphometry, we studied the relationship between gray matter volume in brain areas associated with reward and scores on a behavioral activation system measure (the Sensitivity to Reward scale) in a sample of 50 male undergraduates. Voxel-based morphometry analysis revealed a negative correlation between Sensitivity to Reward scores and gray matter volume in the dorsal striatum and prefrontal cortex. Results indicate that a reduced volume in the striatum might be associated with enhanced reward sensitivity and deficits in inhibitory control.

Behavioral Inhibition System activity is associated with increased amygdala and hippocampal gray matter volume: A voxel-based morphometry study.

Recent research has examined anxiety and hyperactivity in the amygdala and the anterior hippocampus while processing aversive stimuli. In order to determine whether these functional differences have a structural basis, optimized voxel-based morphometry was used to study the relationship between gray matter concentration in the brain and scores on a Behavioral Inhibition System measure (the Sensitivity to Punishment scale) in a sample of 63 male undergraduates. Results showed a positive correlation between Sensitivity to Punishment scores and gray matter volume in the amygdala and the hippocampal formation, that is, in areas that Gray, J.A., and McNaughton, N.J. (2000). The neuropsychology of anxiety. Oxford: Oxford Medical Publications. associated with the Behavioral Inhibition System.

Memory lateralization with 2 functional MR imaging tasks in patients with lesions in the temporal lobe.

BACKGROUND: Previous studies to determine memory lateralization with functional MR imaging (fMRI) have used encoding or recall tasks. The convergence between the results of both tasks, however, is unknown. OBJECTIVE: The objective of this study was to investigate hemispheric asymmetries of temporal lobe activity (parahippocampus and fusiform gyri) in patients with temporal lesions by using both kinds of fMRI tasks. METHODS: By using blood oxygenation level-dependent fMRI, hemispheric asymmetries of 25 consecutive patients admitted for presurgical evaluation of memory and 12 healthy control participants were studied. Activation was induced by using the picture-encoding task (processing of complex scenes) and the hometown-walking task (requiring mental navigation through one's hometown by using landmarks given by participants themselves). RESULTS: Results in the control group showed that both tasks activated the parahippocampus similarly. The picture-encoding task, however, yielded greater posterior activations in the parahippocampus than did the hometown-walking task. As observed in other studies, more than half the patients showed contralesional representation of memory in each task. It is important to note that estimated memory lateralization from each task was different in 30% of patients, and several cases showed clear discrepancies between both tasks. CONCLUSION: Although previous studies showed that both tasks were useful for evaluating memory lateralization, the present study suggested that the administration of both tasks is necessary for presurgical evaluation of memory lateralization in patients with lesions in the temporal lobe. Therefore, both encoding and recall processes should at least be considered in the evaluation of memory.

Cortical reorganization during PASAT task in MS patients with preserved working memory functions.

Cortical reorganization in multiple sclerosis (MS) is defined as a compensatory mechanism which requires MS patients to overactivate specific brain areas in order to perform the task as controls. To investigate this process with the Paced Auditory Serial Addition Test (PASAT) task, we selected 15 MS patients who performed the PASAT task within-normal limits and 10 healthy controls. Once selected, we used functional magnetic resonance imaging (fMRI) to investigate brain areas involved in PASAT performance in both groups. Results showed that the task activated the left frontal (BA6 and 9) and parietal cortex (BA7 and 40) in both groups, but MS patients showed a stronger activation in the left prefrontal cortex (BA9, 44 and 45) when compared with controls. These results confirmed those obtained post hoc by Audoin et al. [Audoin, B., Ibarrola, D., Ranjeva, J.P., Confort-Gouny, S., Malikova, I., Ali-Chérif, A.M., Pelletier, J., Cozzone, P., et al., 2003. Compensatory cortical activation observed by fMRI during cognitive task at the earliest stage of MS. Hum. Brain Mapp. 20, 51-58], and we interpreted this as showing true cortical reorganization.

[Applications of functional magnetic resonance imaging in pre-surgical patients: motor, mnemonic and linguistic functions]. / Aplicaciones de la resonancia magnética funcional en pacientes prequirúrgicos: funciones motora, de memoria y lingüística.

AIMS: This paper reviews and describes cases involving useful protocols for pre-surgical evaluation in functional magnetic resonance imaging (fMRI) of the motor, mnemonic and linguistic functions. DEVELOPMENT: The application of fMRI in pre-surgical evaluation allows us to pinpoint the anatomical location of a function in relation to the lesion. This technique therefore appears as an alternative to the classical intraoperative tests, which are more aggressive and costly. The paper describes aspects and considerations of fMRI with regard to the methodology and procedure employed in its application, as well as the control of contaminating variables that can affect results. The language protocols are described in terms of lateralisation and localisation, and are divided into expressive and receptive language protocols, together with linguistic protocols for overall stimulation that allow the localisation of both expressive and receptive areas. Concerning the motor protocols, we describe the procedures for patients with and without difficulties in their movement. Lastly, we review and describe the memory protocols that give rise to bilateral stimulation in the mesial temporal areas, which allows both lateralisation and localisation of the hippocampal and parahippocampal areas that are functionally significant for the patients' memory. Each of the protocols is illustrated with cases carried out by our work team. CONCLUSIONS: The development of new protocols for pre-surgical evaluation must be guided by greater delimitation and consistency in functional stimulation, as well as analysis of the behaviour displayed.

Aplicaciones de la resonancia magnética funcional en pacientes prequirúrgicos: funciones motora, de memoria y lingüística / Applications of functional magnetic resonance imaging in pre-surgical patients: motor, mnemonic and linguistic functions

Objetivo. Este artículo revisa y presenta casos sobre protocolos útiles de evaluación prequirúrgica en resonancia magnética funcional (RMf) de las funciones motoras, mnésicas y lingüísticas. Desarrollo. La aplicación de la RMf en la evaluación prequirúrgica permite referenciar la localización anatómica de una función en relación con la lesión. En este sentido, esta técnica se plantea como alternativa a las pruebas clásicas intraoperatorias, que son más invasivas y costosas. El artículo reseña aspectos y consideraciones propias de la RMf en relación con su metodología y procedimiento de aplicación, además del control de variables contaminantes que pueden afectar a los resultados. Los protocolos de lenguaje se describen en términos de lateralización y localización, y se distinguen protocolos de lenguaje expresivo y receptivo, además de protocolos lingüísticos de activación global que permiten localizar tanto áreas expresivas como receptivas. En relación con los protocolos motores, se describen los procedimientos para pacientes con y sin dificultades de movimiento. En último lugar, se revisan y describen los protocolos de memoria que producen una activación bilateral en las áreas temporales mesiales, que permiten tanto la lateralización como la localización de las áreas hipocampales y parahipocampales funcionalmente elocuentes para la memoria de los pacientes. Cada uno de los protocolos se ilustra con casos llevados a cabo por nuestro equipo de trabajo. Conclusiones. La mayor delimitación y consistencia en la activación funcional, así como el análisis de la conducta manifiesta, deben guiar el desarrollo de nuevos protocolos de evaluación prequirúrgica (AU)

Aims. This paper reviews and describes cases involving useful protocols for pre-surgical evaluation in functional magnetic resonance imaging (fMRI) of the motor, mnemonic and linguistic functions. Development. The application of fMRI in presurgical evaluation allows us to pinpoint the anatomical location of a function in relation to the lesion. This technique therefore appears as an alternative to the classical intraoperative tests, which are more aggressive and costly. The paper describes aspects and considerations of fRMI with regard to the methodology and procedure employed in its application, as well as the control of contaminating variables that can affect results. The language protocols are described in terms of lateralisation and localisation, and are divided into expressive and receptive language protocols, together with linguistic protocols for overall stimulation that allow the localisation of both expressive and receptive areas. Concerning the motor protocols, we describe the procedures for patients with and without difficulties in their movement. Lastly, we review and describe the memory protocols that give rise to bilateral stimulation in the mesial temporal areas, which allows both lateralisation and localisation of the hippocampal and parahippocampal areas that are functionally significant for the patients’ memory. Each of the protocols is illustrated with cases carried out by our work team. Conclusions. The development of new protocols for pre-surgical evaluation must be guided by greater delimitation and consistence in functional stimulation, as well an analysis of the behaviour displayed (AU)