Tor Endestad

Pupil size signals mental effort deployed during multiple object tracking and predicts brain activity in the dorsal attention network and the locus coeruleus

Attentional effort relates to the allocation of limited-capacity attentional resources to meet current task demands and involves the activation of top-down attentional systems in the brain. Pupillometry is a sensitive measure of this intensity aspect of top-down attentional control. Studies relate pupillary changes in response to cognitive processing to activity in the locus coeruleus (LC), which is the main hub of the brains noradrenergic system and it is thought to modulate the operations of the brains attentional systems. In the present study, participants performed a visual divided attention task known as multiple object tracking (MOT) while their pupil sizes were recorded by use of an infrared eye tracker and then were tested again with the same paradigm while brain activity was recorded using fMRI. We hypothesized that the individual pupil dilations, as an index of individual differences in mental effort, as originally proposed by Kahneman (1973), would be a better predictor of LC activity than the number of tracked objects during MOT. The current results support our hypothesis, since we observed pupil-related activity in the LC. Moreover, the changes in the pupil correlated with activity in the superior colliculus and the right thalamus, as well as cortical activity in the dorsal attention network, which previous studies have shown to be strongly activated during visual tracking of multiple targets. Follow-up pupillometric analyses of the MOT task in the same individuals also revealed that individual differences to cognitive load can be remarkably stable over a lag of several years. To our knowledge this is the first study using pupil dilations as an index of attentional effort in the MOT task and also relating these to functional changes in the brain that directly implicate the LC-NE system in the allocation of processing resources.

Children's usage of media technologies and psychosocial factors

Media use has changed considerably during the past five years and earlier research has produced contradictory results on how media use links to childrens psychosocial factors. This study charts the access to and use of several media technologies among 825 Norwegian schoolchildren between 10 and 12 years of age. The questionnaire contained items concerning childrens self-concept, parental monitoring and social competence. It found that children engage with different kind of media activities and some of these are significantly related to psychosocial factors, however, these correlations were in general quite small. Entertainment usage was associated with low scholastic competence. Both utility usage and heavy advanced usage of new media were related to self-perceptions of athletic competence. Low social acceptance was linked to Gameboy usage and advanced usage of media. Finally, there was a relationship between experienced parental monitoring and utility usage of media technology. The possible implications for these empirical relations are discussed.

What people believe about memory.

Two representative samples of adult Norwegians (n=2000) were asked a set of general and specific questions regarding their beliefs and opinions about human memory. The results indicate that on many questions, such as time of the earliest memories, inhibiting effects of collaboration, and memory for dramatic versus ordinary events, the views of the general public concurred with current research findings, and people in general had realistic views about their own memory performance. On other questions, such as the reliability of olfactory as compared with visual and auditory memory, the memory of small children in comparison with that of adults, the likelihood of repression of adult traumatic memories, and on more general questions such as the possibility of training memory and the capacity limitations of long-term memory, a large proportion of the participants expressed views that are less supported by scientific evidence. Implications of these findings are briefly discussed.

Bright illusions reduce the eye's pupil.

We recorded by use of an infrared eye-tracker the pupil diameters of participants while they observed visual illusions of lightness or brightness. Four original illusions {based on Gaetano Kaniszas [Kanizsa G (1976) Subjective contours. Sci Am 234:48–52] and Akiyoshi Kitaokas [Kitaoka A. (2005) Trick Eyes (Barnes & Noble, New Providence, NJ).] examples} were manipulated to obtain control conditions in which the perceived illusory luminance was either eliminated or reduced. All stimuli were equiluminant so that constrictions in pupillary size could not be ascribed to changes in light energy. We found that the pupillary diameter rapidly varied according to perceived brightness and lightness strength. Differences in local contrast information could be ruled out as an explanation because, in a second experiment, the observers maintained eye fixation in the center of the display; thus, differential stimulation of the fovea by local contrast changes could not be responsible for the pupillary differences. Hence, the most parsimonious explanation for the present findings is that pupillary responses to ambient light reflect the perceived brightness or lightness of the scene and not simply the amount of physical light energy entering the eye. Thus, the pupillary physiological response reflects the subjective perception of light and supports the idea that the brains visual circuitry is shaped by visual experience with images and their possible sources.

Placebo improves pleasure and pain through opposite modulation of sensory processing

Significance Placebo effects illustrate the power of the human brain; simply expecting an improvement can alter pain processing and produce analgesia. We induced placebo improvement of both negative and positive feelings (painful and pleasant touch) in healthy humans, and compared the brain processing using functional MRI. Pain reduction dampened sensory processing in the brain, whereas increased touch pleasantness increased sensory processing. Neurocircuitry associated with emotion and reward underpinned improvement of both pain and pleasant touch. Our findings suggest that expectation of improvement can recruit common neurocircuitry, which up- or down-regulates sensory processing, depending on whether the starting point is painful or pleasant. These results promote widening the scope of medical research to improvement of positive experiences and pleasure. Placebo analgesia is often conceptualized as a reward mechanism. However, by targeting only negative experiences, such as pain, placebo research may tell only half the story. We compared placebo improvement of painful touch (analgesia) with placebo improvement of pleasant touch (hyperhedonia) using functional MRI and a crossover design. Somatosensory processing was decreased during placebo analgesia and increased during placebo hyperhedonia. Both placebo responses were associated with similar patterns of activation increase in circuitry involved in emotion appraisal, including the pregenual anterior cingulate, medial orbitofrontal cortex, amygdala, accumbens, and midbrain structures. Importantly, placebo-induced coupling between the ventromedial prefrontal cortex and periaqueductal gray correlated with somatosensory decreases to painful touch and somatosensory increases to pleasant touch. These findings suggest that placebo analgesia and hyperhedonia are mediated by activation of shared emotion appraisal neurocircuitry, which down- or up-regulates early sensory processing, depending on whether the expectation is reduced pain or increased pleasure.

The role of the lateral prefrontal cortex in inhibitory motor control

Research on inhibitory motor control has implicated several prefrontal as well as subcortical and parietal regions in response inhibition. Whether prefrontal regions are critical for inhibition, attention or task-set representation is still under debate. We investigated the influence of the lateral prefrontal cortex (PFC) in a response inhibition task by using cognitive electrophysiology in prefrontal lesion patients. Patients and age- and education-matched controls performed in a visual Stop-signal task featuring lateralized stimuli, designed to challenge either the intact or lesioned hemisphere. Participants also underwent a purely behavioral Go/Nogo task, which included a manipulation of inhibition difficulty (blocks with 50 vs. 80% go-trials) and a Change-signal task that required switching to an alternative response. Patients and controls did not differ in their inhibitory speed (stop-signal and change-signal reaction time, SSRT and CSRT), but patients made more errors in the Go/Nogo task and showed more variable performance. The behavioral data stress the role of the PFC in maintaining inhibitory control but not in actual inhibition. These results support a dissociation between action cancellation and PFC-dependent action restraint. Laplacian transformed event-related potentials (ERPs) revealed reduced parietal activity in PFC patients in response to the stop-signals, and increased frontal activity over the intact hemisphere. This electrophysiological finding supports altered PFC-dependent visual processing of the stop-signal in parietal areas and compensatory activity in the intact frontal cortex. No group differences were found in the mu and beta decrease as measures of response preparation and inhibition at electrodes over sensorimotor cortex. Taken together, the data provide evidence for a central role of the lateral PFC in attentional control in the context of response inhibition.

Executive functions after orbital or lateral prefrontal lesions: Neuropsychological profiles and self-reported executive functions in everyday living

Objective: This study examined the effects of chronic focal lesions to the lateral prefrontal cortex (LPFC) or orbitofrontal cortex (OFC) on neuropsychological test performance and self-reported executive functioning in everyday living. Methods: Fourteen adults with OFC lesions were compared to 10 patients with LPFC injuries and 21 healthy controls. Neuropsychological tests with emphasis on measures of cognitive executive function were administered along with the Behavior Rating Inventory of Executive Functions (BRIEF-A) and a psychiatric screening instrument. Results: The LPFC group differed from healthy controls on neuropsychological tests of sustained mental effort, response inhibition, working memory and mental switching, while the BRIEF-A provided more clinically important information on deficits in everyday life in the OFC group compared to the LPFC group. Correlations between neuropsychological test results and BRIEF-A were weak, while the BRIEF-A correlated strongly with emotional distress. Conclusions: It was demonstrated that LPFC damage is particularly prone to cause cognitive executive deficit, while OFC injury is more strongly associated with self-reported dysexecutive symptoms in everyday living. The study illustrates the challenge of identifying executive deficit in individual patients and the lack of strong anatomical specificity of the currently employed methods. There is a need for an integrative methodological approach where standard testing batteries are supplemented with neuropsychiatric and frontal-specific rating scales.

Generalized Role for the Cerebellum in Encoding Internal Models: Evidence from Semantic Processing

The striking homogeneity of cerebellar microanatomy is strongly suggestive of a corresponding uniformity of function. Consequently, theoretical models of the cerebellums role in motor control should offer important clues regarding cerebellar contributions to cognition. One such influential theory holds that the cerebellum encodes internal models, neural representations of the context-specific dynamic properties of an object, to facilitate predictive control when manipulating the object. The present study examined whether this theoretical construct can shed light on the contribution of the cerebellum to language processing. We reasoned that the cerebellum might perform a similar coordinative function when the context provided by the initial part of a sentence can be highly predictive of the end of the sentence. Using functional MRI in humans we tested two predictions derived from this hypothesis, building on previous neuroimaging studies of internal models in motor control. First, focal cerebellar activation–reflecting the operation of acquired internal models–should be enhanced when the linguistic context leads terminal words to be predictable. Second, more widespread activation should be observed when such predictions are violated, reflecting the processing of error signals that can be used to update internal models. Both predictions were confirmed, with predictability and prediction violations associated with increased blood oxygenation level-dependent signal in the posterior cerebellum (Crus I/II). Our results provide further evidence for cerebellar involvement in predictive language processing and suggest that the notion of cerebellar internal models may be extended to the language domain.

Contribution of subregions of human frontal cortex to novelty processing

Novelty processing was studied in patients with lesions centered in either OFC or lateral pFC (LPFC). An auditory novelty oddball ERP paradigm was applied with environmental sounds serving as task irrelevant novel stimuli. Lesions to the LPFC as well as the OFC resulted in a reduction of the frontal Novelty P3 response, supporting a key role of both frontal subdivisions in novelty processing. The posterior P3b to target sounds was unaffected in patients with frontal lobe lesions in either location, indicating intact posterior cortical target detection mechanisms. LPFC patients displayed an enhanced sustained negative slow wave (NSW) to novel sounds not observed in OFC patients, indicating prolonged resource allocation to task-irrelevant stimuli after LPFC damage. Both patient groups displayed an enhanced NSW to targets relative to controls. However, there was no difference in behavior between patients and controls suggesting that the enhanced NSW to targets may index an increased resource allocation to response requirements enabling comparable performance in the frontal lesioned patients. The current findings indicate that the LPFC and OFC have partly shared and partly differential contributions to the cognitive subcomponents of novelty processing.

Dissociation of neural correlates of verbal and non-verbal visual working memory with different delays

BackgroundDorsolateral prefrontal cortex (DLPFC), posterior parietal cortex, and regions in the occipital cortex have been identified as neural sites for visual working memory (WM). The exact involvement of the DLPFC in verbal and non-verbal working memory processes, and how these processes depend on the time-span for retention, remains disputed.MethodsWe used functional MRI to explore the neural correlates of the delayed discrimination of Gabor stimuli differing in orientation. Twelve subjects were instructed to code the relative orientation either verbally or non-verbally with memory delays of short (2 s) or long (8 s) duration.ResultsBlood-oxygen level dependent (BOLD) 3-Tesla fMRI revealed significantly more activity for the short verbal condition compared to the short non-verbal condition in bilateral superior temporal gyrus, insula and supramarginal gyrus. Activity in the long verbal condition was greater than in the long non-verbal condition in left language-associated areas (STG) and bilateral posterior parietal areas, including precuneus. Interestingly, right DLPFC and bilateral superior frontal gyrus was more active in the non-verbal long delay condition than in the long verbal condition.ConclusionThe results point to a dissociation between the cortical sites involved in verbal and non-verbal WM for long and short delays. Right DLPFC seems to be engaged in non-verbal WM tasks especially for long delays. Furthermore, the results indicate that even slightly different memory maintenance intervals engage largely differing networks and that this novel finding may explain differing results in previous verbal/non-verbal WM studies.