Staying responsive to the world: modality-specific and -nonspecific contributions to speeded auditory, tactile, and visual stimulus detection

Sustained responsiveness to external stimulation is fundamental to many time-critical interactions with the outside world. We used functional magnetic resonance imaging during speeded stimulus detection to identify convergent and divergent neural correlates of maintaining the readiness to respond to auditory, tactile, and visual stimuli. In addition, using a multimodal condition, we investigated the effect of making stimulus modality unpredictable. Relative to sensorimotor control tasks, all three unimodal detection tasks elicited stronger activity in the right temporo-parietal junction, inferior frontal cortex, anterior insula, dorsal premotor cortex, and anterior cingulate cortex as well as bilateral mid-cingulum, midbrain, brainstem, and medial cerebellum. The multimodal detection condition additionally activated left dorsal premotor cortex and bilateral precuneus. Modality-specific modulations were confined to respective sensory areas: we found activity increases in relevant, and decreases in irrelevant sensory cortices. Our findings corroborate the modality independence of a predominantly right-lateralized core network for maintaining an alert (i.e., highly responsive) state and extend previous results to the somatosensory modality. Monitoring multiple sensory channels appears to induce additional processing, possibly related to stimulus-driven shifts of intermodal attention. The results further suggest that directing attention to a given sensory modality selectively enhances and suppresses sensory processing-even in simple detection tasks, which do not require inter- or intra-modal selection.     

Inconsistency and uncertainty of the human visual area loci following surface-based registration: Probability and Entropy Maps

Here we created two different multisubject maps (16 subjects) to characterize interindividual variability in the positions of human visual areas (V1, dorsal and ventral parts of V2/3, V3A, V3B, V7, LOc, MT+, and hV4 [or V4v and V8]), which were localized using fMRI and coregistered using a surface-based method. The first is a probability map representing the degree of alignment inconsistency for each area, in which each point in space is associated with the probability affiliated with a given area. The second, a novel map termed an entropy map in which each point is associated with Shannon entropy computed from the probabilities, represents the degree of uncertainty regarding the area that resides there, and is maximal when all areas are equally probable. The overall average probability and entropy values were about 0.27 and 1.15 bits, respectively, with dependencies on the visual areas. The probability and entropy maps generated here will benefit any application which requires predictions of areas that are most likely present at an anatomical point and know the uncertainty associated with such predictions.     

fMRI investigation of speed-accuracy strategy switching

Switching between rapid and accurate responses is an important aspect of decision-making. However, the brain mechanisms important to smoothly change the speed-accuracy strategy remain mostly unclear. This issue was addressed here by using functional magnetic resonance imaging (fMRI). On each trial, right-handed healthy participants had to stress speed or accuracy in performing a color discrimination task on a target stimulus according to the instructions given by an initial cue. Participants were capable of trading speed for accuracy and vice versa. Analyses of cue-related fMRI activations revealed a significant recruitment of left middle frontal gyrus and right cerebellum when switching from speed to accuracy. The left superior parietal lobule was activated in the same switching condition but only after the target onset. The anterior cingulate cortex was more recruited, also after target presentation, when speed had to be maintained from one trial to the next. These results are interpreted within a theoretical framework that attributes a role in criterion-setting to the left lateral prefrontal cortex, perceptual evidence accumulation to the superior parietal lobule, and action energization to the anterior cingulate cortex, extending previous findings to the domain of speed-accuracy tradeoff regulations.     

Effects of morphine and alcohol on functional brain connectivity during "resting state": a placebo-controlled crossover study in healthy young men

A major challenge in central nervous system (CNS) drug research is to develop a generally applicable methodology for repeated measurements of drug effects on the entire CNS, without task-related interactions and a priori models. For this reason, data-driven resting-state fMRI methods are promising for pharmacological research. This study aimed to investigate whether different psychoactive substances cause drug-specific effects in functional brain connectivity during resting-state. In this double blind placebo-controlled (double dummy) crossover study, seven resting-state fMRI scans were obtained in 12 healthy young men in three different drug sessions (placebo, morphine and alcohol; randomized). Drugs were administered intravenously based on validated pharmacokinetic protocols to minimize the inter- and intra-subject variance in plasma drug concentrations. Dual-regression was used to estimate whole-brain resting-state connectivity in relation to eight well-characterized resting-state networks, for each data set. A mixed effects analysis of drug by time interactions revealed dissociable changes in both pharmacodynamics and functional connectivity resulting from alcohol and morphine. Post hoc analysis of regions of interest revealed adaptive network interactions in relation to pharmacokinetic and pharmacodynamic curves. Our results illustrate the applicability of resting-state functional brain connectivity in CNS drug research.     

Overnight deprivation from smoking disrupts amygdala responses to fear

Cigarette smoking, a major, yet avoidable, cause of disability and premature death, is the most prevalent form of nicotine addiction. An emerging theme in the neurobiology of nicotine addiction is the integrity of the amygdala. Using functional MRI, amygdala responses during a face perception task were compared between 28 chronic smokers [14 females, 14 males; age, 26.3 (2.8) years; age at onset of smoking, 15.8 (2.6) years; years smoked, 9.1 (2.1); cigarettes per day, 17.1 (3.7); Fagerström test for nicotine dependence score, 4.1 (1.9); exhaled carbon‐monoxide level, 17.8 (9.5) ppm] and 28 age‐ and education‐matched nonsmokers [14 females, 14 males; age, 26.9 (2.4) years]. Subjects underwent imaging on two separate occasions 1 week apart: smoking satiety versus overnight smoking deprivation, in a randomized counterbalanced order. Our results show no difference in amygdala responses to faces between nonsmokers and satiated smokers. However, overnight deprivation from smoking was associated with a significantly lowered amygdala response to fear, an effect that was probabilistically mapped to the basolateral amygdala. We suggest that aberrant amygdala reactivity in overnight‐deprived smokers may reflect a pre‐existing vulnerability to smoking and/or increase the risk of smoking relapse after a cessation attempt. Hum Brain Mapp, 2011. © 2011 Wiley‐Liss, Inc.     

Stimulating creativity via the exposure to other people's ideas

As it is the case in brainstorming, each single idea a person generates to a specific problem may stimulate new ideas or solutions in others. In this fMRI study, we investigate the effects of cognitive stimulation via the exposure to other people's ideas on the originality of generated ideas. Participants are requested to generate alternative uses of conventional everyday objects subsequent to a short cognitive stimulation intervention in which they are exposed to other ideas, which were either common or highly original. In a control condition, meaningless pseudowords are shown. Results suggest that cognitive stimulation via common or moderately creative ideas was effective in improving creativity. At the neurophysiological level, temporo‐parietal brain regions (primarily right‐hemispheric) turned out to be particularly sensitive to cognitive stimulation, possibly indicating that cognitive stimulation via relevant memory cues results in a state of heightened focused attention to memory that facilitates efficient retrieval and recombination of existing knowledge. Hum Brain Mapp, 2012. © 2011 Wiley Periodicals, Inc.     

Degeneration of corpus callosum and recovery of motor function after stroke: A multimodal magnetic resonance imaging study

Animal models of stroke demonstrated that white matter ischemia may cause both axonal damage and myelin degradation distant from the core lesion, thereby impacting on behavior and functional outcome after stroke. We here used parameters derived from diffusion magnetic resonance imaging (MRI) to investigate the effect of focal white matter ischemia on functional reorganization within the motor system. Patients (n = 18) suffering from hand motor deficits in the subacute or chronic stage after subcortical stroke and healthy controls (n = 12) were scanned with both diffusion MRI and functional MRI while performing a motor task with the left or right hand. A laterality index was employed on activated voxels to assess functional reorganization across hemispheres. Regression analyses revealed that diffusion MRI parameters of both the ipsilesional corticospinal tract (CST) and corpus callosum (CC) predicted increased activation of the unaffected hemisphere during movements of the stroke‐affected hand. Changes in diffusion MRI parameters possibly reflecting axonal damage and/or destruction of myelin sheath correlated with a stronger bilateral recruitment of motor areas and poorer motor performance. Probabilistic fiber tracking analyses revealed that the region in the CC correlating with the fMRI laterality index and motor deficits connected to sensorimotor cortex, supplementary motor area, ventral premotor cortex, superior parietal lobule, and temporoparietal junction. The results suggest that degeneration of transcallosal fibers connecting higher order sensorimotor regions constitute a relevant factor influencing cortical reorganization and motor outcome after subcortical stroke. Hum Brain Mapp, 2012. © 2011 Wiley Periodicals, Inc.     

Enhancing the utility of complex-valued functional magnetic resonance imaging detection of neurobiological processes through postacquisition estimation and correction of dynamic B(0) errors and motion

Functional magnetic resonance imaging (fMRI) time series analysis is typically performed using only the magnitude portion of the data. The phase information remains unused largely due to its sensitivity to temporal variations in the magnetic field unrelated to the functional response of interest. These phase changes are commonly the result of physiologic processes such as breathing or motion either inside or outside the imaging field of view. As a result, although the functional phase response carries pertinent physiological information concerning the vasculature, one aspect of which is the location of large draining veins, the full hemodynamic phase response is understudied and is poorly understood, especially in comparison with the magnitude response. It is likely that the magnitude and phase contain disjoint information, which could be used in tandem to better characterize functional hemodynamics. In this work, simulated and human fMRI experimental data are used to demonstrate how statistical analysis of complex-valued fMRI time series can be problematic, and how robust analysis using these powerful and flexible complex-valued statistics is possible through postprocessing with correction for dynamic magnetic field fluctuations in conjunction with estimated motion parameters. These techniques require no special pulse sequence modifications and can be applied to any complex-valued echo planar imaging data set. This analysis shows that the phase component appears to contain information complementary to that in the magnitude and that processing and analysis techniques are available to investigate it in a robust and flexible manner.     

Waiting to win: elevated striatal and orbitofrontal cortical activity during reward anticipation in euthymic bipolar disorder adults

Nusslock R, Almeida JRC, Forbes EE, Versace A, Frank E, LaBarbara EJ, Klein CR, Phillips ML. Waiting to win: elevated striatal and orbitofrontal cortical activity during reward anticipation in euthymic bipolar disorder adults. Bipolar Disord 2012: 14: 249–260. © 2012 The Authors. Journal compilation © 2012 John Wiley & Sons A/S. Objective: Bipolar disorder may be characterized by a hypersensitivity to reward‐relevant stimuli, potentially underlying the emotional lability and dysregulation that characterizes the illness. In parallel, research highlights the predominant role of striatal and orbitofrontal cortical (OFC) regions in reward‐processing and approach‐related affect. We aimed to examine whether bipolar disorder, relative to healthy, participants displayed elevated activity in these regions during reward processing. Methods: Twenty‐one euthymic bipolar I disorder and 20 healthy control participants with no lifetime history of psychiatric disorder underwent functional magnetic resonance imaging (fMRI) scanning during a card‐guessing paradigm designed to examine reward‐related brain function to anticipation and receipt of monetary reward and loss. Data were collected using a 3T Siemens Trio scanner. Results: Region‐of‐interest analyses revealed that bipolar disorder participants displayed greater ventral striatal and right‐sided orbitofrontal [Brodmann area (BA) 11] activity during anticipation, but not outcome, of monetary reward relative to healthy controls (p < 0.05, corrected). Whole‐brain analyses indicated that bipolar disorder, relative to healthy, participants also displayed elevated left‐lateral OFC (BA 47) activity during reward anticipation (p < 0.05, corrected). Conclusions: Elevated ventral striatal and OFC activity during reward anticipation may represent a neural mechanism for predisposition to expansive mood and hypo/mania in response to reward‐relevant cues that characterizes bipolar disorder. Our findings contrast with research reporting blunted activity in the ventral striatum during reward processing in unipolar depressed individuals, relative to healthy controls. Examination of reward‐related neural activity in bipolar disorder is a promising research focus to facilitate identification of biological markers of the illness.