Keeping time: effects of focal frontal lesions

Sustained behaviour: Encoding of cumulative experience in the anterior cingulate

Time is a ubiquitous dimension of behaviour. A new study demonstrates that low-dimensional temporal drift in rodent anterior cingulate ensembles encodes cumulative experience. These data provide fresh insight into how neurons encode extended periods of time to guide high-level behaviours.

Sleep quality and executive function in a diverse sample of healthy young adults

Few studies examine the relationship between sleep and executive function in diverse samples of young adults. Our research aims to fill this gap by analyzing how self-reported sleep quality is related to informant-rated executive function as a whole and its working memory component in a diverse sample of 29 healthy college students. Using the self-report measure, the Pittsburgh Sleep Quality Index (PSQI), we divided our sample into two groups based on cutoff criteria (score ≥5: poor sleep): good sleep quality (n = 11) and poor sleep quality (n = 18). Participants were on average 20.86 years old. Informants rated participants' executive functioning and working memory using the Frontal Systems Behavior Scale (FrSBe) and Behavior Rating Inventory of Executive Function (BRIEF). Individuals in the poor sleep quality group were reported as having significantly worse executive function and working memory scores. Young adult college students who report less than 7 hours of sleep per night have lower scores on informant measures of working memory and executive function. This study raises awareness about how self-reported sleep experiences are related to other's observation of cognitive abilities in everyday life in a diverse young adult sample.

Cathodal high-definition transcranial direct current stimulation (HD-tDCS) of the left ventral prefrontal cortex (vPFC) interferes with conscious error correction

Precise motor timing requires the ability to flexibly adapt one's own movements with respect to changes in the environment. Previous studies suggest that the correction of perceived as compared to non-perceived timing errors involves at least partially distinct brain networks. The dorsolateral prefrontal cortex (dPFC) has been linked to the correction of perceived timing errors and evidence for a contribution of the ventrolateral PFC (vPFC) specifically to the correction of non-perceived errors exists. The present study aimed at clarifying the functional contribution of the left vPFC for the correction of timing errors by adopting high-definition transcranial direct current stimulation (HD-tDCS). Twenty-one young healthy volunteers synchronized their right index finger taps with respect to an isochronous auditory pacing signal. Perceivable and non-perceivable step-changes of the metronome were interspersed, and error correction was analyzed by means of the phase-correction response (PCR). In subsequent sessions anodal and cathodal HD-tDCS was applied to the left vPFC to establish a brain-behavior relationship. Sham stimulation served as control condition. Synchronization accuracy as well as error correction were determined immediately prior to and after HD-tDCS. The analysis suggests a detrimental effect of cathodal HD-tDCS distinctively on error correction in trials with perceived timing errors. The data support the significance of the left vPFC for error correction in the temporal domain but contradicts the view of a role in the correction of non-perceived errors.

Branching Condition of the Color-Word Interference Test Enhances Prediction of Meta-Tasking in Community-Dwelling Older Adults

OBJECTIVES

Meta-tasking (MT) is an aspect of executive functioning (EF) that involves the ability to branch (i.e., to apply "if-then" rules) and to effectively interleave sub-goals of one task with sub-goals of another task. As such, MT is crucial for successful planning, coordination, and execution of multiple complex tasks in daily life. Traditional tests of EF fail to adequately measure MT. This study examined whether Condition 4 of the Color-Word Interference Test (CWIT-4; the inhibition/switching condition that requires branching) predicted MT beyond Condition 3 (CWIT-3; inhibition-only condition) and beyond other subtests from the Delis-Kaplan Executive Function System (D-KEFS) that have a switching condition.

METHOD

Ninety-eight non-Hispanic white community-dwelling older adults completed the first four subtests of the D-KEFS and an ecologically valid measure of MT.

RESULTS

Time to completion and total errors on CWIT-4 accounted for variance in MT above and beyond CWIT-3 and beyond the switching conditions of other D-KEFS subtests. Results remained virtually unchanged when controlling for demographics and general cognitive status.

CONCLUSIONS

Among older adults, CWIT-4 is more strongly associated with MT than other D-KFES tasks. Future research should examine whether CWIT-4 relates to lapses in instrumental activities of daily living among older adults above and beyond other EF tests.

Using Tertiary Sulci to Map the "Cognitive Globe" of Prefrontal Cortex

Stuss considered the human PFC as a "cognitive globe" [Stuss, D. T., & Benson, D. F. Neuropsychological studies of the frontal lobes. Psychological Bulletin, 95, 3-28, 1984] on which functions of the frontal lobe could be mapped. Here, we discuss classic and recent findings regarding the evolution, development, function, and cognitive role of shallow indentations or tertiary sulci in PFC, with the goal of using tertiary sulci to map the "cognitive globe" of PFC. First, we discuss lateral PFC (LPFC) tertiary sulci in classical anatomy and modern neuroimaging, as well as their development, with a focus on those within the middle frontal gyrus. Second, we discuss tertiary sulci in comparative neuroanatomy, focusing on primates. Third, we summarize recent findings showing the utility of tertiary sulci for understanding structural-functional relationships with functional network insights in ventromedial PFC and LPFC. Fourth, we revisit and update unresolved theoretical perspectives considered by C. Vogt and O. Vogt (Allgemeinere ergebnisse unserer hirnforschung. Journal für Psychologie und Neurologie, 25, 279-462, 1919) and F. Sanides (Structure and function of the human frontal lobe. Neuropsychologia, 2, 209-219, 1964) that tertiary sulci serve as landmarks for cortical gradients. Together, the consideration of these classic and recent findings indicate that tertiary sulci are situated in a unique position within the complexity of the "cognitive globe" of PFC: They are the smallest and shallowest of sulci in PFC, yet can offer insights that bridge spatial scales (microns to networks), modalities (functional connectivity to behavior), and species. As such, the map of tertiary sulci within each individual participant serves as a coordinate system specific to that individual on which functions may be further mapped. We conclude with new theoretical and methodological questions that, if answered in future research, will likely lead to mechanistic insight regarding the structure and function of human LPFC.

Rule Perseveration during Task-Switching in Brain Tumor: A Severe Form of Task-Setting Impairment

It has been proposed that at least two distinct processes are engaged during task-switching: reconfiguration of the currently relevant task-set and interference resolution arising from the competing task-set. Whereas in healthy individuals the two are difficult to disentangle, their disruption is thought to cause different impairments in brain-damaged patients. Yet, the observed deficits are inconsistent across studies and do not allow drawing conclusions regarding their independence. Forty-one brain tumor patients were tested on a task-switching paradigm. We compared their performance between switch and repeat trials (switch cost) to assess rule reconfiguration, and between trials requiring the same response (congruent) and a different response for the two tasks (incongruent) to assess interference control. In line with previous studies, we found the greatest proportion of errors on incongruent trials, suggesting an interference control impairment. However, a closer look at the distribution of errors between two task rules revealed a rule perseveration impairment: Patients with high error rate on incongruent trials often applied only one task rule throughout the task and less frequently switched to the alternative one. Multivariate lesion-symptom mapping analysis unveiled the relationship between lesions localized in left orbitofrontal and posterior subcortical regions and perseveration scores, measured as absolute difference in accuracy between two task rules. This finding points to a more severe task-setting impairment, not reflected as a mere switching deficit, but instead as a difficulty in creating multiple stable task representations, in line with recent accounts of OFC functions suggesting its critical role in representing task states.

Time Distortions: A Systematic Review of Cases Characteristic of Alice in Wonderland Syndrome

Of the perceptual distortions characteristic of Alice in Wonderland syndrome, substantial alterations in the immediate experience of time are probably the least known and the most fascinating. We reviewed original case reports to examine the phenomenology and associated pathology of these time distortions in this syndrome. A systematic search in PubMed, Ovid Medline, and the historical literature yielded 59 publications that described 168 people experiencing time distortions, including 84 detailed individual case reports. We distinguished five different types of time distortion. The most common category comprises slow-motion and quick-motion phenomena. In 39% of all cases, time distortions were unimodal in nature, while in 61% there was additional involvement of the visual (49%), kinaesthetic (18%), and auditory modalities (14%). In all, 40% of all time distortions described were bimodal in nature and 19% trimodal, with 1% involving four modalities. Underlying neurological mechanisms are varied and may be triggered by intoxications, infectious diseases, metabolic disorders, CNS lesions, paroxysmal neurological disorders, and psychiatric disorders. Bizarre sensations of time alteration-such as time going backwards or moving in circles-were mostly associated with psychosis. Pathophysiologically, mainly occipital areas appear to be involved, although the temporal network is widely disseminated, with separate component timing mechanisms not always functioning synchronously, thus occasionally creating temporal mismatches within and across sensory modalities (desynchronization). Based on our findings, we propose a classification of time distortions and formulate implications for research and clinical practice.

Medial prefrontal cortex and the temporal control of action

Across species, the medial prefrontal cortex guides actions in time. This process can be studied using behavioral paradigms such as simple reaction-time and interval-timing tasks. Temporal control of action can be influenced by prefrontal neurotransmitters such as dopamine and acetylcholine and is highly relevant to human diseases such as Parkinson's disease, schizophrenia, and attention-deficit hyperactivity disorder (ADHD). We review evidence that across species, medial prefrontal lesions impair the temporal control of action. We then consider neurophysiological correlates in humans, primates, and rodents that might encode temporal processing and relate to cognitive-control mechanisms. These data have informed brain-stimulation studies in rodents and humans that can compensate for timing deficits. This line of work illuminates basic mechanisms of temporal control of action in the medial prefrontal cortex, which underlies a range of high-level cognitive processing and could contribute to new biomarkers and therapies for human brain diseases.

Cerebral Substrates for Controlling Rhythmic Movements

Our daily lives are filled with rhythmic movements, such as walking, sports, and dancing, but the mechanisms by which the brain controls rhythmic movements are poorly understood. In this review, we examine the literature on neuropsychological studies of patients with focal brain lesions, and functional brain imaging studies primarily using finger-tapping tasks. These studies suggest a close connection between sensory and motor processing of rhythm, with no apparent distinction between the two functions. Thus, we conducted two functional brain imaging studies to survey the rhythm representations relatively independent of sensory and motor functions. First, we determined brain activations related to rhythm processing in a sensory modality-independent manner. Second, we examined body part-independent brain activation related to rhythm reproduction. Based on previous literature, we discuss how brain areas contribute rhythmic motor control. Furthermore, we also discuss the mechanisms by which the brain controls rhythmic movements.

Duration reproduction in regular and irregular contexts after unilateral brain damage: Evidence from voxel-based lesion-symptom mapping and atlas-based hodological analysis

It has been proposed that not completely overlapping brain networks support interval timing depending on whether or not an external, predictable temporal cue is provided during the task, aiding time estimation. Here we tested this hypothesis in a neuropsychological study, using both a topological approach - through voxel-based lesion-symptom mapping (VLSM), that assesses the relation between continuous behavioral scores and lesion information on a voxel-by-voxel basis - and a hodological approach, using an atlas-based tractography. A group of patients with unilateral focal brain lesions and their matched controls performed a duration reproduction task assessing time processing in two conditions, namely with regularly spaced stimuli during encoding and reproduction (Regular condition), and with irregularly spaced stimuli during the same task (Irregular condition). VLSM analyses showed that scores in the two conditions were associated with lesions involving partly separable clusters of voxels, with lower performance only in the Irregular condition being related to lesions involving the right insular cortex. Performance in both conditions correlated with the probability of disconnection of the right frontal superior longitudinal tract, and of the superior and middle branches of the right superior longitudinal fasciculus. These findings suggest that the dissociation between timing in regular and irregular contexts is not complete, since performance in both conditions relies on the integrity of a common suprasecond timing network. Furthermore, they are consistent with the hypothesis that tracking time without the aid of external cues selectively relies on the integration of psychophysiological changes in the right insula.

Direct and Indirect Timing Functions in Unilateral Hemispheric Lesions

Introduction

The neural substrates of temporal processing are not still fully known. The majority of interval timing studies have dealt with this subject in the context of "Explicit timing" (computing the time intervals explicitly). The hypothesis "Implicit timing" (implicitly using temporal processing to improve function) has also proposed. This lesion study addressed explicit and implicit timing paradigms simultaneously using identical experimental tasks.

Methods

In this case-control study, 15 patients with Right Hemisphere Damage (RHD) and 15 patients with Left Hemisphere Damage (LHD) and 15 age-matched normal subjects were included. Participants performed a temporal reproduction task (assessing explicit timing) and a temporal prediction task (assessing implicit timing) in two sub- and supra-second intervals.

Results

Our results showed that RHD can lead to significantly lower accuracy in the temporal reproduction task in sub-second (P=0.005) and supra-second (P=0.001) intervals, compared with the normal subjects. Also, LHD led to perturbation in temporal prediction task by an increase in reaction time (lower accuracy) in sub- (P=0.011) and supra-second (P=0.006) time intervals than the normal subjects.

Conclusion

Overall, our findings suggested that there is a right hemispheric bias in the neural substrate of explicit timing, in both sub- and supra-second intervals. Furthermore, for the first time in a lesion study, we showed the evidence of left-hemispheric bias in neural substrates of implicit timing.

Hemispheric asymmetry in the prefrontal cortex for complex cognition

With the exception of language, hemispheric asymmetry has not historically been an important issue in the frontal lobe literature. Data generated over the past 20 years is forcing a reconsideration of this position. There is now considerable evidence to suggest that the left prefrontal cortex is an inference engine that automatically makes simple conceptual, logical, and causal connections to fill in missing information and eliminate uncertainty or indeterminacy. This is a fine-tuning of the "left hemisphere interpreter" account from the callosotomy patient literature. What is new is an understanding of the important contributions of the right prefrontal cortex to formal logical inference, conflict detection, and indeterminacy tolerance and maintenance. This chapter articulates these claims and reviews the data on which they are based. The chapter concludes by speculating that the inference capabilities of the left prefrontal cortex are built into the very fabric of language and can be accounted for by the left hemisphere dominance for language. The roles of the right PFC require multiple mechanisms for explanation. Its role in formal inference may be a function of its visual-spatial processing capabilities. Its role in conflict detection may be explained as a system for checking for consistency between existing beliefs and new information coming into the system and inferences drawn from beliefs and/or new information. There are at least three possible mechanisms to account for its role in indeterminacy tolerance. First, it could contain a representational system with properties very different from those of language, and an accompanying inference engine. Second, it could just contain this different representational system, and the information is at some point passed back to the left prefrontal cortex for inference. Third, the role of the right prefrontal cortex may be largely preventative. That is, it doesn't provide alternative representational and inference capabilities but simply prevents the left prefrontal cortex from settling on initial, local inferences. The current data do not allow differentiating between these possibilities. Successful real-world functioning requires the participation of both hemispheres.

Inactivation of the Medial-Prefrontal Cortex Impairs Interval Timing Precision, but Not Timing Accuracy or Scalar Timing in a Peak-Interval Procedure in Rats

Motor sequence learning, planning and execution of goal-directed behaviors, and decision making rely on accurate time estimation and production of durations in the seconds-to-minutes range. The pathways involved in planning and execution of goal-directed behaviors include cortico-striato-thalamo-cortical circuitry modulated by dopaminergic inputs. A critical feature of interval timing is its scalar property, by which the precision of timing is proportional to the timed duration. We examined the role of medial prefrontal cortex (mPFC) in timing by evaluating the effect of its reversible inactivation on timing accuracy, timing precision and scalar timing. Rats were trained to time two durations in a peak-interval (PI) procedure. Reversible mPFC inactivation using GABA agonist muscimol resulted in decreased timing precision, with no effect on timing accuracy and scalar timing. These results are partly at odds with studies suggesting that ramping prefrontal activity is crucial to timing but closely match simulations with the Striatal Beat Frequency (SBF) model proposing that timing is coded by the coincidental activation of striatal neurons by cortical inputs. Computer simulations indicate that in SBF, gradual inactivation of cortical inputs results in a gradual decrease in timing precision with preservation of timing accuracy and scalar timing. Further studies are needed to differentiate between timing models based on coincidence detection and timing models based on ramping mPFC activity, and clarify whether mPFC is specifically involved in timing, or more generally involved in attention, working memory, or response selection/inhibition.

Fifty Years of Prefrontal Cortex Research: Impact on Assessment

Our knowledge of the functions of the prefrontal cortex, often called executive, supervisory, or control, has been transformed over the past 50 years. After operationally defining terms for clarification, we review the impact of advances in functional, structural, and theoretical levels of understanding upon neuropsychological assessment practice as a means of identifying 11 principles/challenges relating to assessment of executive function. Three of these were already known 50 years ago, and 8 have been confirmed or emerged since. Key themes over this period have been the emergence of the use of naturalistic tests to address issues of "ecological validity"; discovery of the complexity of the frontal lobe control system; invention of new tests for clinical use; development of key theoretical frameworks that address the issue of the role of prefrontal cortex systems in the organization of human cognition; the move toward considering brain systems rather than brain regions; the advent of functional neuroimaging, and its emerging integration into clinical practice. Despite these huge advances, however, practicing neuropsychologists are still desperately in need of new ways of measuring executive function. We discuss pathways by which this might happen, including decoupling the two levels of explanation (information processing; brain structure) and integrating very recent technological advances into the neuropsychologist's toolbox. (JINS, 2017, 23, 755-767).

Altered fronto-striatal functions in the Gdi1-null mouse model of X-linked Intellectual Disability

RAB-GDP dissociation inhibitor 1 (GDI1) loss-of-function mutations are responsible for a form of non-specific X-linked Intellectual Disability (XLID) where the only clinical feature is cognitive impairment. GDI1 patients are impaired in specific aspects of executive functions and conditioned response, which are controlled by fronto-striatal circuitries. Previous molecular and behavioral characterization of the Gdi1-null mouse revealed alterations in the total number/distribution of hippocampal and cortical synaptic vesicles as well as hippocampal short-term synaptic plasticity, and memory deficits. In this study, we employed cognitive protocols with high translational validity to human condition that target the functionality of cortico-striatal circuitry such as attention and stimulus selection ability with progressive degree of complexity. We previously showed that Gdi1-null mice are impaired in some hippocampus-dependent forms of associative learning assessed by aversive procedures. Here, using appetitive-conditioning procedures we further investigated associative learning deficits sustained by the fronto-striatal system. We report that Gdi1-null mice are impaired in attention and associative learning processes, which are a key part of the cognitive impairment observed in XLID patients.

Clock Speed as a Window into Dopaminergic Control of Emotion and Time Perception

Although fear-producing treatments (e.g., electric shock) and pleasure-inducing treatments (e.g., methamphetamine) have different emotional valences, they both produce physiological arousal and lead to effects on timing and time perception that have been interpreted as reflecting an increase in speed of an internal clock. In this commentary, we review the results reported by Fayolle et al. (2015):Behav. Process., 120, 135–140) and Meck (1983: J. Exp. Psychol. Anim. Behav. Process., 9, 171–201) using electric shock and by Maricq et al. (1981: J. Exp. Psychol. Anim. Behav. Process., 7, 18–30) using methamphetamine in a duration-bisection procedure across multiple duration ranges. The psychometric functions obtained from this procedure relate the proportion ‘long’ responses to signal durations spaced between a pair of ‘short’ and ‘long’ anchor durations. Horizontal shifts in these functions can be described in terms of attention or arousal processes depending upon whether they are a fixed number of seconds independent of the timed durations (additive) or proportional to the durations being timed (multiplicative). Multiplicative effects are thought to result from a change in clock speed that is regulated by dopamine activity in the medial prefrontal cortex. These dopaminergic effects are discussed within the context of the striatal beat frequency model of interval timing (Matell & Meck, 2004:Cogn. Brain Res.,21, 139–170) and clinical implications for the effects of emotional reactivity on temporal cognition (Parker et al., 2013:Front. Integr. Neurosci., 7, 75).

Ramping activity is a cortical mechanism of temporal control of action

A fundamental feature of the mammalian cortex is to guide movements in time. One common pattern of neural activity observed across cortical regions during temporal control of action is ramping activity. Ramping activity can be defined as consistent increases or decreases in neuronal firing rate across behaviorally relevant epochs of time. Prefrontal brain regions, including medial frontal and lateral prefrontal cortex, are critical for temporal control of action. Ramping is among the most common pattern of neural activity in these prefrontal areas during behavioral tasks. Finally, stimulating prefrontal neurons in medial frontal cortex can influence the timing of movement. These data can be helpful in approaching human diseases with impaired temporal of action, such as Parkinson's disease and schizophrenia. Cortical ramping activity might contribute to new diagnostic and therapeutic strategies for these and other debilitating human diseases.

Contribution of Cerebellar Loops to Action Timing

Recent studies of sensorimotor processing have benefited from decision-making paradigms that emphasize the selection of appropriate movements. Selecting when to make those responses, or action timing, is important as well. Although the cerebellum is commonly viewed as a controller of movement dynamics, its role in action timing is also firmly supported. Several lines of research have now extended this idea. Anatomical findings have revealed connections between the cerebellum and broader timing circuits, neurophysiological results have suggested mechanisms for timing within its microcircuitry, and theoretical work has indicated how temporal signals are processed through it and decoded by its targets. These developments are inspiring renewed studies of the role of the cerebellar loops in action timing.

Latent profiles of executive functioning in healthy young adults: evidence of individual differences in hemispheric asymmetry

Two competing theoretical models of individual differences in executive functioning (EF) were examined: the Prefrontal Convexity Model and the Hemispheric Asymmetry Model. Neurologically healthy individuals (N = 315; mean age 20.8) completed a modified switching task (MST) and the Attention Network Test (ANT) in a single testing session. Data analysis was conducted in two phases. In the first phase (model identification), latent profile analysis was applied to MST variables measuring the abilities to form, switch, and maintain mental sets under conditions designed to tax left or right hemisphere resources. In the second phase (model validation), participant clusters obtained from the first phase were compared on the ANT. The Model Identification phase yielded a 3-profile solution consistent with the Hemispheric Asymmetry Model. Profile 1 (N = 203) was characterized by average EF performances. Profile 2 (N = 43) revealed a set maintenance weakness under non-verbal conditions. Profile 3 (N = 38) demonstrated weaknesses in cognitive flexibility combined with poor executive performances under verbal conditions. The Model Validation phase confirmed group differences. Profile 1 demonstrated average EF performances. Profile 2 demonstrated distractibility and decreased alertness, consistent with a right hemisphere weakness. Profile 3 demonstrated cognitive rigidity in the absence of external cues, consistent with a left hemisphere weakness. Individual differences in EF appear to follow a Hemispheric Asymmetry Model of EF among neurologically healthy adults. Investigating the relationship between hemispherically mediated executive functions and other individual difference factors known to confer health risk or resilience could inform numerous disciplines within the field of psychology.

Internally and externally generated emotions in people with acquired brain injury: preservation of emotional experience after right hemisphere lesions

The study of emotional changes after brain injury has contributed enormously to the understanding of the neural basis of emotion. However, little attention has been placed on the methods used to elicit emotional responses in people with brain damage. Of particular interest are subjects with right hemisphere [RH] cortical lesions, who have been described as presenting impairment in emotional processing. In this article, an internal and external mood induction procedure [MIP] was used to trigger positive and negative emotions, in a sample of 10 participants with RH damage, and 15 healthy controls. Emotional experience was registered by using a self-report questionnaire. As observed in previous studies, internal and external MIPs were equally effective in eliciting the target emotion, but the internal procedure generated higher levels of intensity. Remarkably, participants with RH lesions were equally able to experience both positive and negative affect. The results are discussed in relation to the role of the RH in the capacity to experience negative emotions.

Propositional speech in unselected stroke: The effect of genre and external support

Distinguished from nominal language, propositional language generation refers to the spontaneous and voluntary aspect of language that introduces novel concepts to a specific context. Propositional language can be impaired in a range of neurological disorders, including stroke, despite well-preserved nominal language. Although external support can increase speech rate in patients with reduced propositional speech, no specific investigation of propositional speech has been carried out in unselected stroke patients. The current study investigated propositional language in an unselected post-acute stroke group (N = 18) with mild cognitive impairment and prominent executive dysfunction, but without significant aphasia. Specifically, we investigated whether genre or external support affected the number of words, sentences, and novel ideas produced, compared to healthy controls (N = 27). Results showed that discourse genre was not associated with differential performances. By contrast, speech quantity increased without external support although, for stroke patients, speech novelty decreased. Overall, the novelty deficit in unselected stroke patients highlights the importance of assessing cognition and propositional speech. Our findings suggest that for stroke patients with mild cognitive deficits, including executive dysfunction, introducing external support improved speech quality but not quantity. Implications for both assessment and rehabilitation of social communication are discussed.

The impact of frontal and cerebellar lesions on decision making: evidence from the Iowa Gambling Task

Although the frontal lobes have traditionally been considered the neural substrates of executive functioning (EF), recent studies have suggested that other structures, such as the cerebellum, may be associated with these abilities. The role of the cerebellum has only been sparsely investigated in connection with decision making (DM), an important component of EF, and the few results obtained on this front have been inconclusive. The current study sought to investigate the role of the cerebellum in DM by comparing the performance of patients with cerebellar strokes, frontal-damaged patients, and a healthy control group on the Iowa Gambling Task (IGT). A total of nine cerebellar-damaged adults participated in the study, as well as nine individuals with frontal strokes and 18 control individuals. Patients were administered a version of the IGT adapted to the population of Southern Brazil. There was a marginal difference in mean IGT net scores between the two clinical groups, although both displayed impaired performance as compared to the control group. Overall, the DM ability of patients with cerebellar damage proved to be more preserved than that of individuals with frontal lobe strokes, but less preserved than that of the control group. These data suggested that, while the frontal lobes may be the most important brain structures for DM, the cerebellum might also play an active role in this cognitive function. Future studies assessing participants with lesions in different cerebellar regions and hemispheres will prove invaluable for the understanding of the neural structures involved in DM, and make significant contributions to the globalist-localizationist debate in DM neuroscience.

Serotonergic hallucinogens as translational models relevant to schizophrenia

One of the oldest models of schizophrenia is based on the effects of serotonergic hallucinogens such as mescaline, psilocybin, and (+)-lysergic acid diethylamide (LSD), which act through the serotonin 5-HT(2A) receptor. These compounds produce a 'model psychosis' in normal individuals that resembles at least some of the positive symptoms of schizophrenia. Based on these similarities, and because evidence has emerged that the serotonergic system plays a role in the pathogenesis of schizophrenia in some patients, animal models relevant to schizophrenia have been developed based on hallucinogen effects. Here we review the behavioural effects of hallucinogens in four of those models, the receptor and neurochemical mechanisms for the effects and their translational relevance. Despite the difficulty of modelling hallucinogen effects in nonverbal species, animal models of schizophrenia based on hallucinogens have yielded important insights into the linkage between 5-HT and schizophrenia and have helped to identify receptor targets and interactions that could be exploited in the development of new therapeutic agents.

Impaired Representation of Time in Schizophrenia Is Linked to Positive Symptoms and Cognitive Demand

Time processing critically relies on the mesencephalic dopamine system and striato-prefrontal projections and has thus been suggested to play a key role in schizophrenia. Previous studies have provided evidence for an acceleration of the internal clock in schizophrenia that may be linked to dopaminergic pathology. The present study aimed to assess the relationship between altered time processing in schizophrenia and symptom manifestation in 22 patients and 22 controls. Subjects were required to estimate the time needed for a visual stimulus to complete a horizontal movement towards a target position on trials of varying cognitive demand. It was hypothesized that patients – compared to controls – would be less accurate at estimating the movement time, and that this effect would be modulated by symptom manifestation and task difficulty. In line with the notion of an accelerated internal clock due to dopaminergic dysregulation, particularly patients with severe positive symptoms were expected to underestimate movement time. However, if altered time perception in schizophrenia was better explained in terms of cognitive deficits, patients with severe negative symptoms should be specifically impaired, while generally, task performance should correlate with measures of processing speed and cognitive flexibility. Patients underestimated movement time on more demanding trials, although there was no link to disease-related cognitive dysfunction. Task performance was modulated by symptom manifestation. Impaired estimation of movement time was significantly correlated with PANSS positive symptom scores, with higher positive symptom scores associated with stronger underestimation of movement time. The present data thus support the notion of a deficit in anticipatory and predictive mechanisms in schizophrenia that is modulated both by symptom manifestation and by cognitive demand.

Time discrimination in traumatic brain injury patients

Time management skills are required for most daily activities. Traumatic brain injury (TBI) patients often present with cognitive dysfunction, but few studies have investigated temporal impairment. The aim of the present study was to assess temporal abilities in TBI patients using a time discrimination task. Twenty-seven TBI patients (ages = 18-60 years) and 27 controls (ages = 20-60 years) were asked to discriminate between two time intervals presented sequentially. The standard intervals were 500 ms or 1,300 ms long followed by a comparison stimulus that was 25% shorter or longer than the standard one. Participants were also asked to perform two tasks to assess attention, speed-of-processing (the Stroop task), and working memory (the n-back task) abilities. The TBI patients were less accurate than the controls on the time discrimination task and showed greater time-order error effects. In fact, TBI patients pressed the "short" key more times when the standard time interval was 500 ms and the "long" key more times when the standard interval was 1,300 ms. Significant correlations were found between time discrimination, working memory, and speed of processing in both TBI and controls when the standard time interval was 1,300 ms. Attention appeared to be involved in different ways in the two groups. Working memory and speed of processing were involved in time processing only in TBI patients when the standard time interval was 500 ms. These data lend additional support to the notion that two different systems are responsible for elaborating time durations shorter or longer than a second.

The impact of depression heterogeneity on cognitive control in major depressive disorder

OBJECTIVE

Depressed patients display a variety of deficits in neuropsychological function, and contradictory findings in the literature may be due to disorder heterogeneity. The aim of this study was to examine the impact of severity, subtype and symptoms on cognitive control.

METHODS

Neuropsychological function across a range of cognitive control tasks was examined in melancholic (n = 65) and non-melancholic depressed patients (n = 59) relative to controls (n = 124). The relationship between subtype (melancholia vs non-melancholia) and anxiety was also examined.

RESULTS

Melancholia was characterised by attention and working memory deficits typically associated with the dorsolateral prefrontal cortex, while non-melancholia was characterised by verbal memory recall deficits indicative of left frontal lobe and medial temporal lobe function. The severity of anxious arousal and psychomotor disturbance contributed to cognitive impairment more than the severity of depression symptoms and anxious apprehension.

CONCLUSIONS

Findings highlight a differential impact of depression subtype and severity, and suggest that anxious arousal and psychomotor disturbance may contribute to poorer performance on neuropsychological tasks associated with dorsolateral prefrontal cortex function.

The differing roles of the frontal cortex in fluency tests

Fluency tasks have been widely used to tap the voluntary generation of responses. The anatomical correlates of fluency tasks and their sensitivity and specificity have been hotly debated. However, investigation of the cognitive processes involved in voluntary generation of responses and whether generation is supported by a common, general process (e.g. fluid intelligence) or specific cognitive processes underpinned by particular frontal regions has rarely been addressed. This study investigates a range of verbal and non-verbal fluency tasks in patients with unselected focal frontal (n=47) and posterior (n=20) lesions. Patients and controls (n=35) matched for education, age and sex were administered fluency tasks including word (phonemic/semantic), design, gesture and ideational fluency as well as background cognitive tests. Lesions were analysed by standard anterior/posterior and left/right frontal subdivisions as well as a finer-grained frontal localization method. Thus, patients with right and left lateral lesions were compared to patients with superior medial lesions. The results show that all eight fluency tasks are sensitive to frontal lobe damage although only the phonemic word and design fluency tasks were specific to the frontal region. Superior medial patients were the only group to be impaired on all eight fluency tasks, relative to controls, consistent with an energization deficit. The most marked fluency deficits for lateral patients were along material specific lines (i.e. left-phonemic and right-design). Phonemic word fluency that requires greater selection was most severely impaired following left inferior frontal damage. Overall, our results support the notion that frontal functions comprise a set of specialized cognitive processes, supported by distinct frontal regions.

Timing as a window on cognition in schizophrenia

Distorted interval timing is a common feature of the cognitive impairment observed in patients with schizophrenia. The neural circuits which are required for interval timing and those thought to be compromised in schizophrenia overlap and include the cortico-striatal pathways. Here, we suggest that a focus on temporal information processing offers a window into understanding the cognitive deficits of schizophrenia and how deficits might contribute to a variety of symptoms. A disruption in the functioning of the cortico-striatal pathways may lead to cognitive deficits which in turn lead to impaired processing of temporal information. Disrupted temporal processing may also contribute to a variety of other symptoms associated with the disorder. Because interval timing is a cognitive/behavioral phenotype that can easily be assessed in animals it can be used as a sensitive screen for deficits in animal models. Using a recently developed transgenic mouse that models increased D2 receptor upregulation in the striatum similar to that observed in patients with schizophrenia we illustrate the utility of an interval timing approach in assessing cognitive impairment. We further discuss how variants of timing procedures can be used to assess attention and working memory performance as well as other necessary components of adaptive cognitive function.

Event-related potential study of frontal activity during imagination of rhythm

In 11 healthy volunteers, we used event-related potentials (ERP) to investigate the frontal activity associated with imagining a beat. In imagery sessions, subjects were asked to imagine a rhythm during a silent recording period following a series of guide sounds played at 1 Hz. In control sessions, subjects were asked to imagine a vowel sound ("a") continuously during the silent recording period. In eight subjects, relative negative potentials were recorded during imagery sessions (compared with potentials in control sessions), with timing that was similar to that of the guide sounds. Activity in the left frontal region was more significant than that in other areas during beat imagination. These data indicate that a semantic strategy for simple rhythm imagery might involve temporary phasic activation in the left frontal area, although rhythm production and perception might be generated in the right side, as reported in previous studies.

Temporal discrimination of sub- and suprasecond time intervals: a voxel-based lesion mapping analysis

We used voxel-based lesion-symptom mapping (VLSM) to determine which brain areas are necessary for discriminating time intervals above and below 1 s. VLSM compares behavioral scores of patients that have damage to a given voxel to those that do not on a voxel-by-voxel basis to determine which voxels are critical for the given behavior. Forty-seven subjects with unilateral hemispheric lesions performed a temporal discrimination task in which a standard stimulus was compared on each trial to a test stimulus. In different blocks of trials, standard stimuli were either 600 or 2000 ms. Behavioral measures included the point of subjective equality, a measure of accuracy, and the coefficient of variation, a measure of variability. Lesions of the right middle and inferior frontal gyri were associated with decrements in performance on both durations. In addition, lesions of the left temporal lobe and right precentral gyrus were associated exclusively with impaired performance for subsecond stimuli. In line with results from other studies, these data suggest that different circuits are necessary for timing intervals in these ranges, and that right frontal areas are particularly important to timing.

The future of cognitive neurorehabilitation

Cognitive neurorehabilitation is rooted both in the cognitive function being treated and the neural substrates underlying that ability. Recent progress in understanding both brain (in particular brain plasticity) and the complexities of behaviour imply a promising future for cognitive neurorehabilitation. The manuscripts in this issue focuse on advances in the use of non-invasive brain stimulation (NIBS) as a tool for cognitive neurorehabilitation. This paper presents a broader context in which to understand the importance and potential of this specific approach. Achieving the promise requires theoretical and experimental rigour including selection of relevant outcome measures, and understanding of the complexities of individual patients. Success will depend on our ability to integrate knowledge and approaches.

Functions of the frontal lobes: relation to executive functions

Proceeding from the assumptions that specific frontal regions control discrete functions and that very basic cognitive processes can be systematically manipulated to reveal those functions, recent reports have demonstrated consistent anatomical/functional relationships: dorsomedial for energization, left dorsolateral for task setting, and right dorsolateral for monitoring. There is no central executive. There are, instead, numerous domain general processes discretely distributed across several frontal regions that act in concert to accomplish control. Beyond these functions, there are two additional "frontal" anatomical/functional relationships: ventral-medial/orbital for emotional and behavioral regulation, and frontopolar for integrative-even meta-cognitive-functions.

The role of rostral prefrontal cortex in prospective memory: a voxel-based lesion study

Patients with lesions in rostral prefrontal cortex (PFC) often experience problems in everyday-life situations requiring multitasking. A key cognitive component that is critical in multitasking situations is prospective memory, defined as the ability to carry out an intended action after a delay period filled with unrelated activity. The few functional imaging studies investigating prospective memory have shown consistent activation in both medial and lateral rostral PFC but also in more posterior prefrontal regions and non-frontal regions. The aim of this study was to determine regions that are necessary for prospective memory performance, using the human lesion approach. We designed an experimental paradigm allowing us to assess time-based (remembering to do something at a particular time) and event-based (remembering to do something in a particular situation) prospective memory, using two types of material, words and pictures. Time estimation tasks and tasks controlling for basic attention, inhibition and multiple instructions processing were also administered. We examined brain-behaviour relationships with a voxelwise lesion method in 45 patients with focal brain lesions and 107 control subjects using this paradigm. The results showed that lesions in the right polar prefrontal region (in Brodmann area 10) were specifically associated with a deficit in time-based prospective memory tasks for both words and pictures. This deficit could not be explained by impairments in basic attention, detection, inhibition or multiple instruction processing, and there was also no deficit in event-based prospective memory conditions. In addition to their prospective memory difficulties, these polar prefrontal patients were significantly impaired in time estimation ability compared to other patients. The same region was found to be involved using both words and pictures, suggesting that right rostral PFC plays a material nonspecific role in prospective memory. This is the first lesion study showing that rostral PFC is crucial for time-based prospective memory. The findings suggest that time-based and event-based prospective memory might be supported at least in part by distinct brain regions. Two particularly plausible explanations for the deficit rest upon a possible role for polar prefrontal structures in supporting in time estimation, and/or in retrieving an intention to act. More broadly, the results are consistent with the view that the deficit of rostral patients in multitasking situations might at least in part be explained by a deficit in prospective memory.

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.

Frontal subregions mediating Elevator Counting task performance

Deficits in sustained attention may lead to action slips in everyday life as irrelevant action sequences are inappropriately triggered internally or by the environment. While deficits in sustained attention have been associated with damage to the frontal lobes of the brain, little is known about the role of the frontal lobes in the Elevator Counting subtest of the Test of Everyday Attention. In the current study, 55 frontal patients subdivided into medial, orbital and lateral subgroups, 18 patients with posterior lesions and 82 healthy controls performed the Elevator Counting task. The results revealed that patients with medial and left lateral prefrontal lesions were significantly impaired on the task compared to healthy controls. Research suggests that patients with medial lesions are susceptible to competition from task irrelevant schema; whereas the left lateral group in the current study may fail to keep track of the tones already presented.

Effects of somatosensory stimulation and attention on human somatosensory cortex: an fMRI study

It is well known that primary and non-primary areas of human somatosensory cortex are involved in the processing of adequate deviant/rare stimuli and omission of frequent stimuli. However, the relative weight and interaction of these variables is poorly known. This functional magnetic resonance imaging (fMRI) study tested the hypothesis that somatosensory stimulus processing and attention especially interact in non-primary somatosensory areas including secondary somatosensory cortex (SII) and insula. To test this hypothesis, responses of somatosensory cortex were mapped during four conditions of an oddball paradigm: DELIVERED COUNT and IGNORE (count or ignore deviant/rare electrical stimuli, respectively); OMITTED COUNT and IGNORE (count or ignore the rare omission of frequent electrical stimuli, respectively). The deviant/rare and frequent electrical stimuli were delivered to median and ulnar nerve, respectively. It was observed that contralateral (left) primary somatosensory responses were not markedly modulated by the mentioned deviant/rare events. Furthermore, contralateral SII and insula responded to all but not OMITTED IGNORE (purely attentive) condition, whereas ipsilateral (right) SII responded to all conditions. Finally, ipsilateral insula responded to the COUNT (attentive) conditions, regardless of the physical presence of the deviant/rare stimuli. The results suggest that in somatosensory modality, bilateral SII and left (contralateral) insula reflect complex integrative processes of stimulus elaboration and attention, whereas right (ipsilateral) insula mainly sub-serves active attention to deviance within a sequence of somatosensory stimuli.

Changing time and emotions

In this paper, we consider that our experience of time (to come) depends on the emotions we feel when we imagine future pleasant or unpleasant events. A positive emotion such as relief or joy associated with a pleasant event that will happen in the future induces impatience. Impatience, in our context, implies that the experience of time up to the forthcoming event expands. A negative emotion such as grief or frustration associated with an unpleasant event that will happen in the future triggers anxiety. This will give the experience of time contraction. Time, therefore, is not exogeneously given to the individual and emotions, which link together events or situations, are a constitutive ingredient of the experience of time. Our theory can explain experimental evidence that people tend to prefer to perform painful actions earlier than pleasurable ones, contrary to the predictions yielded by the standard exponential discounting framework.

Stroke and episodic memory disorders

Memory impairments are common after stroke, and the anatomical basis for impairments may be quite variable. To determine the range of stroke-related memory impairment, we identified all case reports and group studies through the Medline database and the Science Citation Index. There is no hypothesis about memory that is unique to stroke, but there are several important facets of memory impairment after stroke: (1) Every node of the limbic system implicated in memory may be damaged by stroke but very rarely in isolation and the combination of amnesia with the associated deficits often illuminates additional aspects of memory functions. (2) Stroke produces amnesia by damage to critical convergence white matter connections of the limbic system, and stroke is the only etiology of amnesia that can delineate the entire pathway of memory and critical convergence points. (3) Stroke also impairs memory, without causing classical amnesia, by damaging brain regions responsible for cognitive processes, some modality specific and some more generally strategic, that are essential for normal learning and recall.

Impaired List Learning Is Not a General Property of Frontal Lesions

Background: List-learning tasks are frequently used to provide measures of “executive functions” that are believed necessary for successful memory performance. Small sample sizes, confounding anomia, and incomplete representation of all frontal regions have prevented consistent demonstration of distinct regional frontal effects on this task. Objective: To confirm specific effects of lesions in different frontal regions. Subjects: Forty-one patients with chronic focal frontal lesions and 38 control subjects. There were no group differences in naming scores. Methods: Two word lists were presented, one with unblocked words from related categories and one in a preblocked format. Standard measures of learning, recall, recognition, and strategies were obtained, first for the frontal group as a whole and then for large but defined frontal regions. For all measures with significant group differences, a lesion “hotspotting” method identified possible specific regional injury effects. Results: The frontal group was impaired on almost all measures, but impairments on most measures were particularly identified with lesions in the left superior frontal lobe (approximately area 9s) and some deficits in learning processes were surprisingly more prominent on the blocked list. Conclusion: Difficulty with list learning is not a general property of all frontal lesions. Lesions in different frontal regions impair list learning through specific mechanisms, and these effects may be modified by manipulations of the task structure.