A role for the right prefrontal and bilateral parietal cortex in four-term transitive reasoning: an fMRI study with abstract linear syllogism tasks

Previous imaging studies have identified many brain regions activated during reasoning, but there are differences among the findings concerning specific regions engaged in reasoning and the contribution of language areas. Also, little is known about the relation between task complexity and neural activation during reasoning. The present fMRI study investigated brain activity during complex four-term transitive reasoning with abstract material (determinate or partially indeterminate) and compared the resulting images to those obtained during a memorization task. The memory condition required subjects to memorize unrelated elements whereas the reasoning conditions required them to integrate information from premises and to infer relations between elements. After contrasting the two kinds of reasoning conditions with the memory condition we found that right prefrontal and bilateral parietal regions are specifically activated during reasoning. We also demonstrated that different reasoning requirements--the possibility of constructing one (determined reasoning) versus several (undetermined reasoning) models of a situation during task solving--lead to different patterns of brain activity, with higher prefrontal (PFC) activity accompanying undetermined reasoning. We interpret the PFC activity as a reflection of simultaneous maintenance and manipulation of information in reasoning. These findings provide new evidence that specific forms of reasoning (abstract and undetermined) demand recruitment of right PFC and hemispheric coordination and lend new support to the mental model theory of relational reasoning.     

Brain oscillation and connectivity during a chemistry visual working memory task

Many studies have reported that frontal theta and posterior alpha activities are associated with working memory tasks. However, fewer studies have focused on examining whether or not the frontal alpha or posterior theta can play a role in the working memory task. This study investigates electroencephalography (EEG) dynamics and connectivity among different brain regions' theta and alpha oscillations. The EEG was collected from undergraduate students (n = 64) while they were performing a Sternberg-like working memory task involving chemistry concepts. The results showed that the frontal midline cluster exhibited sustained theta augmentation across the periods of stimulus presentations, maintenance, and probe presentation, suggesting that the frontal midline theta might associate with facilitating the central execute function to maintain information in the working memory. Study of the central parietal and the occipital clusters revealed a sequence of theta augmentation followed by alpha suppression at constant intervals after the onset of stimulus and probe presentations, suggesting that the posterior theta might be associated with sensory processing, theta gating, or stimulus selection. It further suggests that the posterior alpha event-related de-synchronization (ERD) might be linked to direct information flow into and out of the long-term memory (LTM) and precede stimulus recognition. An alternating phasic alpha event-related synchronization (ERS) and ERD following the 1st stimulus and probe presentations were observed at the occipital cluster, in which alpha ERS might be linked to the inhibition of irrelevant information.     

Brain regions and their dynamics in prospective memory retrieval: a MEG study.

We measured brain activity using magnetoencephalography in five participants during ongoing tasks that included prospective memory, retrospective memory, and oddball trials. Sources were identified in the hippocampal formation and posterior parietal and frontal lobes. Posterior parietal cortex activation had an earlier onset in the prospective memory condition than retrospective memory or oddball conditions, a higher level of theta activity in the retrospective condition, and higher levels of upper alpha in the prospective and oddball conditions. Activation of the hippocampal formation had a longer duration in the retrospective memory and prospective memory conditions than the oddball condition, but prominent alpha and theta band activity was present in all three conditions. We interpret the early (87 ms) onset of activity in parietal cortex as evidence for an initial noticing of appropriate conditions for a PM response. Hippocampal activity may reflect a subsequent memory search for the intended action.     

High-Resolution EEG Analysis of Power Spectral Density Maps and Coherence Networks in a Proportional Reasoning Task

Proportional reasoning is very important logical skill required in mathematics and science problem solving as well as in everyday life decisions. However, there is a lack of studies on neurophysiological correlates of proportional reasoning. To explore the brain activity of healthy adults while performing a balance scale task, we used high-resolution EEG techniques and graph-theory based connectivity analysis. After unskilled subjects learned how to properly solve the task, their cortical power spectral density (PSD) maps revealed an increased parietal activity in the beta band. This indicated that subjects started to perform calculations. In addition, the number of inter-hemispheric connections decreased after learning, implying a rearrangement of the brain activity. Repeated performance of the task led to the PSD decrease in the beta and gamma bands among parietal and frontal regions along with a synchronization of lower frequencies. These findings suggest that repetition led to a more automatic task performance. Subjects were also divided in two groups according to their scores on the test of logical thinking (TOLT). Although no group differences in the accuracy and reaction times were found, EEG data showed higher activity in the beta and gamma bands for the group that scored better on TOLT. Learning and repetition induced changes in the pattern of functional connectivity were evident for all frequency bands. Overall, the results indicated that higher frequency oscillations in frontal and parietal regions are particularly important for proportional reasoning.     

Effects of induced fatigue on brain activity during sensorimotor control

The aim of this study was to study if accuracy in sensorimotor control and cortical activity was influenced after induced fatigue during a knee joint reproduction task. Twelve volunteers performed a sensorimotor task before, directly after and 60 min after a prolonged exhaustive exercise protocol. The task consisted of an active reproduction of a target knee angle. After three practice trials, visual feedback was taken and the task was performed for 10 repetitions at a suitable pace. Reproduction accuracy was analyzed and EEG raw data were obtained from the frontal, central, temporal, parietal and occipital scalp locations during the task. The average power spectra in theta and alpha frequencies were computed across conditions for each participant. Task accuracy decreases significantly related to fatigue and increases after recovery. This is accompanied by a significant decrease in frontal theta, alpha-1 and alpha-2 frequencies after inducing fatigue. The power values in all frequency bands recovered after 60 min. Sensorimotor control was influenced by induced fatigue, which could be demonstrated in behavior and brain activity. Characteristics of brain activity demonstrated an increase in theta and a decrease in alpha-1 and alpha-2 frequency band power. The changes were discussed related to attentional recourses, alertness and somatosensory information processing mechanisms.     

Relevance of EEG alpha and theta oscillations during task switching

In a task switching design, we investigated the question whether long-range theta coupling primarily reflects top–down control processes. Switch and stay trials did not differ with respect to memory load or global working memory (WM) demands. The results revealed significantly stronger theta coupling (in a range of 4–7 Hz) between prefrontal and posterior regions during switch as compared to stay trials. Power differences, reflecting more local effects, were largest in the upper alpha band (10–13 Hz) and over posterior brain areas, possibly reflecting long-term memory activation. The conclusion of the present study is that long-range coherent oscillatory activity in the theta band reflects top–down activation rather than global WM functions.     

Transverse patterning dissociates human EEG theta power and hippocampal BOLD activation

Theta oscillations (4-8 Hz) are often modulated in human electroencephalogram (EEG) studies of memory, whereas overlapping frequencies dominate rodent hippocampal EEG. An emerging parallelism between theta reactivity and hippocampal functional magnetic resonance imaging activation has suggested a homology between theta activity in humans and rodents, representing a process of cortico-hippocampal interaction involved in memory. In the present study, we investigated EEG reactivity during performance of a relational memory task that induces a negative hippocampal blood oxygenation level dependent (BOLD) signal change, compared to a nonrelational control condition. Relational trials induced theta increases and alpha decreases. Low Resolution Electromagnetic Brain Tomography estimates localized theta and alpha modulation to frontal midline and parietal midline cortices, respectively, both of which exhibit negative BOLD responses in this task. Thus, theta and alpha dynamics are dissociable from positive BOLD activation, and may, in fact, colocalize with negative BOLD responses.     

Cortical areas related to performance of WAIS Digit Symbol Test: A functional imaging study

Many neuropsychological studies have shown that the Digit Symbol Test (DST) of the Wechsler Adult Intelligence Scale (WAIS) is useful for screening for dysfunctions of the brain. However, it remains unclear which brain areas are actually involved in the performance of DST and what brain functions are used for executing this test. In this study, we examined the cortical areas related to cognitive aspects of DST using functional magnetic resonance imaging (fMRI) and determined executive brain functions involved in this test on the basis of fMRI results. Eleven healthy young adults (mean = 21.6 years) performed a modified DST (mDST) task and its control task, which required a simple graphomotor response during fMRI data acquisition. The direct comparison of brain activations between the mDST task and the control task revealed greater activations in a fronto-parietal cortical network, including the bilateral inferior frontal sulci, left middle frontal gyrus (close to the frontal eye field) and left posterior parietal cortex. These activations are interpreted as reflecting the visual search process and/or the updating process of working memory during the mDST task execution. Furthermore, we found a positive correlation between the number of correct responses and activations in the bilateral inferior frontal regions, suggesting that these prefrontal areas have a crucial role in the performance of DST in a healthy young adult population.     

Development of working memory maintenance

The neural circuitry supporting mature visual spatial working memory (VSWM) has been well delineated in nonhuman primates and in human adults. However, we still have limited understanding about developmental change through adolescence in this network. We present results from a fast event-related functional MRI (fMRI) study aimed at characterizing developmental changes in brain mechanisms supporting VSWM across different delay periods. Forty-three healthy subjects (17 adults, 18-30 yr; 13 adolescents, 13-17 yr; 13 children, 8-12 yr) were scanned as they performed an oculomotor delayed response (ODR) task with short (2.5 s) and long (10 s) delay period trials. Results showed that all age groups recruited a common network of regions to support both delay trials, including frontal, parietal, and temporal regions, indicative of a core circuitry needed to perform the task. Several age-related differences were found in the recruitment of regions, supporting short delay trials, including fronto-caudal areas, which could contribute to known differences in initial memory-guided saccade precision. To support extended delay trials, adults primarily recruited additional posterior parietal cortex (PPC), whereas children and adolescents recruited a considerably more extensive distributed circuitry. Our findings indicate that brain processes supporting basic aspects of working memory across cortex are established by childhood. We also find evidence for continued immaturities in systems supporting working memory precision, reflected by differences in the circuitry recruited by children and by continued refinement of fronto-insular-temporal regions recruited by adolescents. Taken together, these results suggest distinct developmental changes in the circuitry supporting visual spatial working memory.     

Verbal working memory‐related neural network communication in schizophrenia

Impaired working memory (WM) in schizophrenia is associated with reduced hemodynamic and electromagnetic activity and altered network connectivity within and between memory‐associated neural networks. The present study sought to determine whether schizophrenia involves disruption of a frontal‐parietal network normally supporting WM and/or involvement of another brain network. Nineteen schizophrenia patients (SZ) and 19 healthy comparison subjects (HC) participated in a cued visual‐verbal Sternberg task while dense‐array EEG was recorded. A pair of item arrays each consisting of 2–4 consonants was presented bilaterally for 200 ms with a prior cue signaling the hemifield of the task‐relevant WM set. A central probe letter 2,000 ms later prompted a choice reaction time decision about match/mismatch with the target WM set. Group and WM load effects on time domain and time‐frequency domain 11–15 Hz alpha power were assessed for the cue‐to‐probe time window, and posterior 11–15 Hz alpha power and frontal 4–8 Hz theta power were assessed during the retention period. Directional connectivity was estimated via Granger causality, evaluating group differences in communication. SZ showed slower responding, lower accuracy, smaller overall time‐domain alpha power increase, and less load‐dependent alpha power increase. Midline frontal theta power increases did not vary by group or load. Network communication in SZ was characterized by temporal‐to‐posterior information flow, in contrast to bidirectional temporal‐posterior communication in HC. Results indicate aberrant WM network activity supporting WM in SZ that might facilitate normal load‐dependent and only marginally less accurate task performance, despite generally slower responding.     

Electroencephalographic Evidence of Altered Top–Down Attentional Modulation in Fibromyalgia Patients During a Working Memory Task

Fibromyalgia (FM) is a chronic syndrome involving widespread pain of unclear pathophysiology. FM patients frequently complain about cognitive symptoms that interfere with their daily life activities. Several studies have reported attentional deficits and working memory impairment in FM patients. Nevertheless, the mechanisms involved in these alterations are still poorly understood. In this study we recorded electroencephalographic activity in 32 women with FM and 30 matched controls while they performed a 2-back working memory task. We analyzed behavioural data, posterior alpha and midfrontal theta frequency power, and theta phase synchronization between midfrontal locations and the remaining scalp-recorded areas. Task performance was similar in patients and controls; however, time–frequency analysis showed a smaller decrease in the amplitude of the posterior alpha (related to attentional processing) and a smaller increase in midfrontal theta power (related to mental effort) in FM patients than in healthy controls. The FM patients also showed lower functional connectivity between midfrontal locations and rest of the scalp-recorded areas in the theta band (related to information transfer across distant brain regions when top-down control is required). To our knowledge, this is the first study relating alterations in oscillatory activity and impaired connectivity to attentional working memory complaints in FM patients. Reduced power in the theta band during performance of the task suggests that the medial frontal cortex may play an important role in the attentional deficits reported in FM.     

Prefrontal and parietal contributions to spatial working memory

Functional neuroimaging studies consistently implicate a widespread network of human cortical brain areas that together support spatial working memory. This review summarizes our recent functional magnetic resonance imaging studies of humans performing delayed-saccades. These studies have isolated persistent activity in dorsal prefrontal regions, like the frontal eye fields, and the posterior parietal cortex during the maintenance of positional information. We aim to gain insight into the type of information coded by this activity. By manipulating the sensory and motor demands of the working memory task, we have been able to modulate the frontal eye fields and posterior parietal cortex delay-period activity. These findings are discussed in the context of other neurophysiological and lesion-based data and some hypotheses regarding the differential contributions of frontal and parietal areas to spatial working memory are offered. Namely, retrospective sensory coding of space may be more prominent in the posterior parietal cortex, while prospective motor coding of space may be more prominent in the frontal eye fields.     

Brain regions concerned with perceptual skills in tennis: an fMRI study.

Sporting performance makes special demands on perceptual skills, but the neural mechanisms underlying such performance are little understood. We address this issue, making use of fMRI to identify the brain areas activated in viewing and responding to video sequences of tennis players, filmed from the opponent's perspective. In a block-design, fMRI study, 9 novice tennis players watched video clips of tennis play. The main stimulus conditions were (1) serve sequences, (2) non-serve behaviour (ball bouncing) and (3) static control sequences. A button response was required indicating the direction of serve (left or right for serve sequences, middle button for non-serve and static sequences). By comparing responses to the three stimulus conditions, it was possible to identify two groups of brain regions responsive to different components of the task. Areas MT/MST and STS in the posterior part of the temporal lobe responded either to serve and to non-serve stimuli, relative to static controls. Serve sequences produced additional regions of activation in the parietal lobe (bilateral IPL, right SPL) and in the right frontal cortex (IFGd, IFGv), and these areas were not activated by non-serve sequences. These regions of the parietal and frontal cortex have been implicated in a "mirror neuron" network in the human brain. It is concluded that the task of judgement of serve direction produces two different patterns of response: activations in the MT/MST and STS concerned with primarily with the analysis of motion and body actions, and activations in the parietal and frontal cortex associated specifically with the task of identification of direction of serve.     

Memory activation in healthy nonagenarians

Little is known about brain function in the oldest old, although this is the fastest growing segment of the population in developed countries and is of paramount importance in public health considerations. In this study, we investigated the cerebral response to a memory task in healthy subjects over age 90 compared with healthy younger elderly.We studied 29 healthy elderly subjects, 12 over age 90 and 17 between age 70 and 80. All subjects were cognitively intact, as verified by a neuropsychological battery, and performed a nonverbal memory task while undergoing a functional MRI (fMRI). Activation results were analyzed by a random-effects ANCOVA using SPM5. The task resulted in activation of similar areas of the posterior temporal, parietal, and posterior frontal cortexes, but the activation was more robust in the younger subjects, especially in the right hippocampus, and parietal and temporal cortices. This finding remained after controlling for education, cognition, task performance or cerebral atrophy.The phenomenon of relatively maintained performance, despite significant brain atrophy and lower activation is consistent with the cognitive reserve theory and may be specific to subjects with extremely successful aging. Further investigation of brain activation patterns in the oldest old is warranted.     

Frontal theta and posterior alpha in resting EEG: A critical examination of convergent and discriminant validity

Prior research has identified two resting EEG biomarkers with potential for predicting functional outcomes in depression: theta current density in frontal brain regions (especially rostral anterior cingulate cortex) and alpha power over posterior scalp regions. As little is known about the discriminant and convergent validity of these putative biomarkers, a thorough evaluation of these psychometric properties was conducted toward the goal of improving clinical utility of these markers. Resting 71-channel EEG recorded from 35 healthy adults at two sessions (1-week retest) were used to systematically compare different quantification techniques for theta and alpha sources at scalp (surface Laplacian or current source density [CSD]) and brain (distributed inverse; exact low resolution electromagnetic tomography [eLORETA]) level. Signal quality was evaluated with signal-to-noise ratio, participant-level spectra, and frequency PCA covariance decomposition. Convergent and discriminant validity were assessed within a multitrait-multimethod framework. Posterior alpha was reliably identified as two spectral components, each with unique spatial patterns and condition effects (eyes open/closed), high signal quality, and good convergent and discriminant validity. In contrast, frontal theta was characterized by one low-variance component, low signal quality, lack of a distinct spectral peak, and mixed validity. Correlations between candidate biomarkers suggest that posterior alpha components constitute reliable, convergent, and discriminant biometrics in healthy adults. Component-based identification of spectral activity (CSD/eLORETA-fPCA) was superior to fixed, a priori frequency bands. Improved quantification and conceptualization of frontal theta is necessary to determine clinical utility.     

Interactions of cognitive reserve with regional brain anatomy and brain function during a working memory task in healthy elders

Cognitive reserve (CR) defines the capacity of the adult brain to cope with pathology in order to minimize symptomatology. Relevant lifetime social, cognitive and leisure activities represent measurable proxies of cognitive CR but its underlying structural and functional brain mechanisms remain poorly understood. We investigated the relationship between CR and regional gray matter volumes and brain activity (fMRI) during a working memory task in a sample of healthy elders. Participants with higher CR had larger gray matter volumes in frontal and parietal regions. Conversely, a negative correlation was observed between CR and fMRI signal in the right inferior frontal cortex, suggesting increased neural efficiency for higher CR individuals. This latter association however disappeared after adjusting for gray matter images in a voxel-based manner. Altogether, present results may reflect both general and specific anatomofunctional correlates of CR in the healthy elders. Thus, whereas heteromodal anterior and posterior gray matter regions correspond to passive (i.e. morphological) correlates of CR unrelated to functional brain activation during this particular cognitive task, the right inferior frontal area reveals interactions between active and passive components of CR related to the cognitive functions tested in the fMRI study.     

Brain electrical activity signatures during performance of the Multisource Interference Task

The Multisource Interference Task (MSIT) was developed to test cognitive control in normal and pathological conditions and has become a reliable tool for exploring the integrity of cingulo‐frontal‐parietal cognitive/attentional networks in fMRI studies. Analysis of EEG recordings made during performance of the MSIT may provide additional information about the temporal dynamics of cognitive control. However, this has not yet been investigated in depth. In this study, we analyzed the ERPs and carried out time‐frequency decomposition of EEG recorded during control and interference conditions of the MSIT. The N2 ERP component and midfrontal theta power (both considered neural signatures of conflict processing) were significantly larger in interference than in control trials. Theta also showed higher phase synchronization between midfrontal and right frontolateral scalp locations in the interference condition, supporting the view that this frequency band entrains additional brain resources when a need for greater control arises. In interference trials, we also observed longer P3 latency, larger P3 amplitude, and greater reduction of posterior alpha (modulations related to allocation of attentional resources), in addition to a greater reduction of central beta power (related to motor preparation). In conclusion, the MSIT reliably modulated brain electrical activity related to cognitive control and attention. The EEG indices obtained during the performance of this task may be useful for exploring the functioning of cognitive/attentional networks in healthy and clinical populations.     

Multivariate analysis of EEG coherence: stability of the metric, individual differences in patterning and response to arousal

When coherence is computed among all pairs of a multichannel EEG, the resultant matrix can be de-structured with conventional multivariate analysis procedures to characterize the patterning of electrophysiologic information at each frequency band of the EEG across brain regions. Six right-handed young men had EEG data recorded from left and right frontal, temporal, parietal, and occipital locations during three visits to the laboratory at one week intervals. During each session, data were recorded during a relaxation period, an alert resting period, and as loud white noise was presented. Factor analysis of coherence matrices showed a model pattern of a large posterior factor and an anterior factor, both of which were right-lateralized, plus a residual factor that was most often left-lateralized. Four of the six men showed this pattern on each occasion, particularly for the delta and the theta bands. Two men showed variant patterns, which were also stable over time. A priori de-structuring of the matrix into partial multiple intrahemispheric and inter-hemispheric coherences also showed generally higher coherences on the right side, with the exception of left occipital inter-hemispheric values. Effects of arousal manipulations were not striking, but the factor patterns suggested increases in right hemisphere coherence for the alpha and beta bands during high arousal.     

Oscillatory gamma and theta activity during repeated mental manipulations of a visual image

Previous studies on mental manipulation have dealt with direct manipulation of a presented stimulus or a maintained image of a previously presented stimulus. Here, we investigated brain activity differences between successive maintenance and manipulation of the visual stimulus and the once transformed representations using electroencephalography (EEG) in a multi-stage sequential manipulation task. The task required the subjects to memorize a presented object which possessed four features (color, shape, direction and speed of motion) and transform the feature of the representation twice. Wavelet analysis showed strong gamma-band (>30 Hz) activity elicited in the frontal and parietal regions during two successive mental manipulation tasks of the visual stimulus. Interestingly, gamma activity in the frontal and parietal regions was stronger during the second manipulation. Our results suggest that successive mental manipulations of the once transformed representation may impose higher demand on the fronto-parietal networks. On the other hand, while the frontal theta activity was enhanced throughout maintenance and manipulation periods, the activity during maintenance of one-time manipulated representation was higher than that of the physically presented stimulus, suggesting that the frontal regions are further recruited in maintenance of manipulated images.     

Vascular health risks and fMRI activation during a memory task in older adults

Vascular problems increase Alzheimer's disease (AD) risk, but the nature of this relationship remains unclear. Older adults having genetic risk for AD show regionally increased functional magnetic resonance imaging (fMRI) activity during memory, possibly representing compensation for a genetically induced neural deficit. We investigated whether vascular health risks, which similarly could lead to neuropsychological deficits, also showed increased fMRI activity during a memory task performed by 30 cognitively intact, primarily normotensive older adults (mean age=61). Vascular risk measures included systolic blood pressure (sBP), body mass index (BMI), and total cholesterol. Higher sBP and BMI (but not total cholesterol) were significantly correlated with increased activation in posterior cingulate cortex and frontal, temporal, and parietal regions. In posterior cingulate and parietal cortices, these relationships were evident even within sBP and BMI ranges considered normal, and were independent of hippocampal volume. Our results are similar to those in prior AD risk research, and suggest that fMRI reveals an abnormal response to cognitive processes in cognitively intact older adults with increased vascular risk.