Mario Liotti

An ERP study of the temporal course of the Stroop color-word interference effect

The electrophysiological correlates of the Stroop color-word interference effect were studied in eight healthy subjects using high-density Event-Related Potentials (ERPs). Three response modalities were compared: Overt Verbal, Covert Verbal, and Manual. Both Overt Verbal and Manual versions of the Stroop yielded robust Stroop color-word interference as indexed by longer RT for incongruent than congruent color words. The Incongruent vs Congruent ERP difference wave presented two effects. A first effect was a medial dorsal negativity between 350-500 ms post-stimulus (peak at 410 ms). This effect had a significantly different scalp distribution in the Verbal and Manual Stroop versions, with an anterior-medial focus for overt or covert speech, and a broader medial-dorsal distribution for the manual task. Dipole source analysis suggested two independent generators in anterior cingulate cortex. Later on in time, a prolonged positivity developed between 500-800 ms post-stimulus over left superior temporo-parietal scalp. This effect was present for all the three response modalities. A possible interpretation of these results is that Stroop color-word interference first activates anterior cingulate cortex (350-500 ms post-stimulus), followed by activation of the left temporo-parietal cortex, possibly related to the need of additional processing of word meaning.

Inhibitory control in children with attention-deficit/hyperactivity disorder: event-related potentials identify the processing component and timing of an impaired right-frontal response-inhibition mechanism.

BACKGROUND A core deficit in inhibitory control may account for a wide range of dysfunctional behaviors in attention-deficit/hyperactivity disorder (ADHD). METHODS Event-related potentials were measured in 10 children with ADHD and 10 healthy children during a task specifically involving response inhibition (Stop signal task). RESULTS In response to all Stop signals, control participants produced a large negative wave at 200 msec (N200) over right inferior frontal cortex, which was markedly reduced in ADHD children. The N200 amplitude was significantly correlated across subjects with response-inhibition performance. In response to the Go stimuli, ADHD children showed a reduced slow positive wave (250-500 msec) in anticipation of failed inhibitions over right frontal scalp regions. CONCLUSIONS ADHD children appear to have an abnormality in an early-latency, right inferior frontal processing component critical to the initiation of normal response-inhibition operations. They also appear to have a right frontal abnormality associated to the covert processing of Go stimuli preceding failed inhibitions. By providing timing and processing component specificity, these results extend the findings of recent functional MRI studies of inhibitory control reporting right frontal abnormalities in ADHD.

Differential limbic–cortical correlates of sadness and anxiety in healthy subjects: implications for affective disorders

BACKGROUND Affective disorders are associated with comorbidity of depression and anxiety symptoms. Positron emission tomography resting-state studies in affective disorders have generally failed to isolate specific symptom effects. Emotion provocation studies in healthy volunteers have produced variable results, due to differences in experimental paradigm and instructions. METHODS To better delineate the neural correlates of sad mood and anxiety, this study used autobiographical memory scripts in eight healthy women to generate sadness, anxiety, or a neutral relaxed state in a within-subject design. RESULTS Sadness and anxiety, when contrasted to a neutral emotional state, engaged a set of distinct paralimbic-cortical regions, with a limited number of common effects. Sadness was accompanied by specific activations of the subgenual cingulate area (BA) 25 and dorsal insula, specific deactivation of the right prefrontal cortex BA 9, and more prominent deactivation of the posterior parietal cortex BAs 40/7. Anxiety was associated with specific activations of the ventral insula, the orbitofrontal and anterior temporal cortices, specific deactivation of parahippocampal gyri, and more prominent deactivation of the inferior temporal cortex BAs 20/37. CONCLUSIONS These findings are interpreted within a model in which sadness and anxiety are represented by segregated corticolimbic pathways, where a major role is played by selective dorsal cortical deactivations during sadness, and ventral cortical deactivations in anxiety.

The role of functional neuroimaging in the neuropsychology of depression

Depressed individuals show impaired performance in tests of attention and concentration. They also exhibit PET resting state abnormalities in dorsal prefrontal cortex and anterior cingulate, regions known to be substrates of attentional processing in healthy individuals. This chapter outlines a strategy to study neuropsychological mechanisms in emotional disorders using functional imaging methods. It reviews evidence strongly implicating the dorsolateral prefrontal cortex, particularly in the right hemisphere, as a key brain structure in emotion/cognition interactions in negative mood states. It will be argued that this neocortical region is a crucial convergence zone, being the substrate of sustained attention to the external environment, and the main target of limbic-cortical influences during changes in mood state across health and disease.

Semantic amnesia with preservation of autobiographic memory. A case report.

A 44-year-old woman showed, following an episode of encephalitis, an impoverished knowledge of the meaning and attributes of words and their referents, in spite of intact command of grammatical-syntactic rules and preserved perceptual abilities. There was also a complete loss of the stock of notions she had acquired over her life and constituting the cultural background of a person, in contrast with normal memory for autobiographic events. The case is interpreted as an instance of semantic amnesia. MRI showed damage confined to the antero-medial part of the left temporal lobe.

Naturalizing aesthetics: Brain areas for aesthetic appraisal across sensory modalities

We present here the most comprehensive analysis to date of neuroaesthetic processing by reporting the results of voxel-based meta-analyses of 93 neuroimaging studies of positive-valence aesthetic appraisal across four sensory modalities. The results demonstrate that the most concordant area of activation across all four modalities is the right anterior insula, an area typically associated with visceral perception, especially of negative valence (disgust, pain, etc.). We argue that aesthetic processing is, at its core, the appraisal of the valence of perceived objects. This appraisal is in no way limited to artworks but is instead applicable to all types of perceived objects. Therefore, one way to naturalize aesthetics is to argue that such a system evolved first for the appraisal of objects of survival advantage, such as food sources, and was later co-opted in humans for the experience of artworks for the satisfaction of social needs.

Task-Related Default Mode Network Modulation and Inhibitory Control in ADHD: Effects of Motivation and Methylphenidate.

BACKGROUND Deficits characteristic of attention deficit/hyperactivity disorder (ADHD), including poor attention and inhibitory control, are at least partially alleviated by factors that increase engagement of attention, suggesting a hypodopaminergic reward deficit. Lapses of attention are associated with attenuated deactivation of the default mode network (DMN), a distributed brain system normally deactivated during tasks requiring attention to the external world. Task-related DMN deactivation has been shown to be attenuated in ADHD relative to controls. We hypothesised that motivational incentives to balance speed against restraint would increase task engagement during an inhibitory control task, enhancing DMN deactivation in ADHD. We also hypothesised that methylphenidate, an indirect dopamine agonist, would tend to normalise abnormal patterns of DMN deactivation. METHOD We obtained functional magnetic resonance images from 18 methylphenidate-responsive children with ADHD (DSM-IV combined subtype) and 18 pairwise-matched typically developing children aged 9-15 years while they performed a paced Go/No-go task. We manipulated motivational incentive to balance response speed against inhibitory control, and tested children with ADHD both on and off methylphenidate. RESULTS When children with ADHD were off-methylphenidate and task incentive was low, event-related DMN deactivation was significantly attenuated compared to controls, but the two groups did not differ under high motivational incentives. The modulation of DMN deactivation by incentive in the children with ADHD, off-methylphenidate, was statistically significant, and significantly greater than in typically developing children. When children with ADHD were on-methylphenidate, motivational modulation of event-related DMN deactivation was abolished, and no attenuation relative to their typically developing peers was apparent in either motivational condition. CONCLUSIONS During an inhibitory control task, children with ADHD exhibit a raised motivational threshold at which task-relevant stimuli become sufficiently salient to deactivate the DMN. Treatment with methylphenidate normalises this threshold, rendering their pattern of task-related DMN deactivation indistinguishable from that of typically developing children.

Hypophonia in Parkinson’s disease: Neural correlates of voice treatment revealed by PET

Objective: To investigate the neural correlates of hypophonia in individuals with idiopathic PD (IPD) before and after voice treatment with the Lee Silverman Voice Treatment method (VT) using 15O-H2O PET. Methods: Regional cerebral blood flow (rCBF) changes associated with overt speech–motor tasks relative to the resting state were measured in the IPD subjects before and after VT, and in a group of healthy control volunteers. Results: Behavioral measures of voice loudness significantly improved following treatment. Before VT, patients had strong speech-related activations in motor and premotor cortex (M1-mouth, supplementary motor cortex [SMA], and inferior lateral premotor cortex [ILPm]), which were significantly reduced post-VT. Similar to the post-treatment session, premotor activations were absent (SMA) or below statistical threshold (M1-mouth) in the healthy control group. In addition, following VT treatment, significant right-sided activations were present in anterior insular cortex, caudate head, putamen, and dorsolateral prefrontal cortex (DLPFC). Finally, the VT-induced neural changes were not present with transient experimenter-cued increases of loudness in VT-untreated patients. Conclusions: Effective improvement of IPD hypophonia following voice treatment with VT was accompanied by a reduction of cortical motor–premotor activations, resembling the functional pattern observed in healthy volunteers and suggesting normalization, and additional recruitment of right anterior insula, caudate head, putamen, and DLPFC. This treatment-dependent functional reorganization suggests a shift from an abnormally effortful (premotor cortex) to a more automatic (basal ganglia, anterior insula) implementation of speech–motor actions.

Volumetric MRI differences in treatment-naïve vs chronically treated children with ADHD

Objective: To determine if there are differences in the volume of the caudate and anterior cingulate cortex (ACC) between children with attention deficit hyperactivity disorder (ADHD) and controls, and if such differences are related to the subjects’ history of stimulant treatment. Methods: We performed a case-control study in an academic medical center. Twenty-one healthy controls, 16 children with ADHD, combined type with a history of stimulant treatment, and 14 children with ADHD, combined type treatment naïve, underwent structural MRI. All children with ADHD were medication-free at the time of the MRI. Regional hemispheric volumes (in cm3) of caudate and anterior cingulate cortex were determined. Results: There were significant differences bilaterally on caudate volume for both ADHD groups vs controls, with no difference between the ADHD groups on either side. In contrast, the right ACC was significantly smaller for the ADHD-treatment naïve (ADHD/TN) group compared to the ADHD-treated (ADHD/Rx) and control group. The volume of left ACC approached significance contrast between ADHD/RX and ADHD/TN. There were no differences found between the ADHD/Rx and controls on the ACC volumes bilaterally. Conclusions: The results from this study indicate a relationship of previous treatment history with caudate and anterior cingulate volumetric changes in children with attention deficit hyperactivity disorder–combined type.

Frontal and inferior temporal cortical activity in visual target detection: Evidence from high spatially sampled event-related potentials

SummaryVisual event-related potential (ERP) studies show effects due to target detection in the P3 and in earlier negativities over posterior recording sites. The topography of these earlier components suggests contributions from both anterior and posterior neural generators, however these studies were performed with sparse recording arrays and may not have provided a full description of the scalp topography of the visual ERP. The current study employed a high-density recording array (64 channels) and spherical spline interpolated topographic voltage and current density maps to describe the scalp distribution of the major deflections in the visual ERP from a visual oddball paradigm: the P1, N1, N2/P2a (a temporally coincident posterior negativity and anterior positivity) and P3. A modified difference wave analysis was also performed to track the time-course of target detection effects in the ERP. Target detection effects were found in the N2/P2a and P3 components. The scalp distribution of the N2/P2a was consistent with separate frontal and posterior neural generators and this is discussed in reference to human hemodynamic and nonhuman primate studies of neural activity in the inferior temporal visual object recognition system and in frontal systems of selective attention and working memory in visual target detection tasks.