Very Early Brain Damage Leads to Remodeling of the Working Memory System in Adulthood: A Combined fMRI/Tractography Study.

The human brain can adapt to overcome injury even years after an initial insult. One hypothesis states that early brain injury survivors, by taking advantage of critical periods of high plasticity during childhood, should recover more successfully than those who suffer injury later in life. This hypothesis has been challenged by recent studies showing worse cognitive outcome in individuals with early brain injury, compared with individuals with later brain injury, with working memory particularly affected. We invited individuals who suffered perinatal brain injury (PBI) for an fMRI/diffusion MRI tractography study of working memory and hypothesized that, 30 years after the initial injury, working memory deficits in the PBI group would remain, despite compensatory activation in areas outside the typical working memory network. Furthermore we hypothesized that the amount of functional reorganization would be related to the level of injury to the dorsal cingulum tract, which connects medial frontal and parietal working memory structures. We found that adults who suffered PBI did not significantly differ from controls in working memory performance. They exhibited less activation in classic frontoparietal working memory areas and a relative overactivation of bilateral perisylvian cortex compared with controls. Structurally, the dorsal cingulum volume and hindrance-modulated orientational anisotropy was significantly reduced in the PBI group. Furthermore there was uniquely in the PBI group a significant negative correlation between the volume of this tract and activation in the bilateral perisylvian cortex and a positive correlation between this activation and task performance. This provides the first evidence of compensatory plasticity of the working memory network following PBI.

Electrophysiological indices of interference resolution covary with individual fluid intelligence: investigating reactive control processes in a 3-back working memory task.

It has been proposed that the well-established relationship between working memory (WM) and fluid intelligence (gf) is mediated by executive mechanisms underlying interference control. The latter relies upon the integrity of a frontoparietal brain network, whose activity is modulated by general cognition. In regards to the chronology of this activation, only few EEG studies investigated the topic, although none of them examined the regional interaction or the effects of individual differences in gf. The current investigation sought at extending previous research by characterizing the EEG markers (temporal activation and regional coupling) of interference control and the effects of the individual variation in gf. To this end, we recorded the EEG activity of 33 participants while performing verbal and spatial versions of a 3-back WM task. In a separate session, participants were administered with a test of fluid intelligence. Interference-inducing trials were associated with an increased negativity in the frontal scalp region occurring in two separate time windows and probably reflecting two different stages of the underlying cognitive process. In addition, we found that scalp distribution of such activity differed among individuals, being the strongest activation of the left and right frontolateral sites related to high gf level. Finally, high- and low-gf participants showed different patterns in the modulation of regional connectivity (electrodes coherence in the range of 4.5-7.5Hz) according to changes in attention load among types of trials. Our findings suggest that high-gf participants may rely upon effective engagement and modulation of attention resources to face interference.

Schizotypal traits and neuropsychological performance: The role of processing speed.

BACKGROUND: Cognitive deficits, particularly in processing speed, are widely recognized as a critical feature of schizophrenia, and are also present across schizophrenia spectrum disorders. A number of important confounders, however, such as hospitalization effects and antipsychotic medication, have been shown to affect processing speed, causing debate as to the core cognitive deficits of schizophrenia. The study of individuals who are not clinically psychotic but have schizotypal traits allows investigation of cognitive deficits associated with both positive and negative schizotypy dimensions while excluding potential confounds. METHODS: A population-based community sample of 242 healthy adult volunteers assessed using the Structured Interview of Schizotypy - Revised (SIS-R) scale, and a neuropsychological testing battery that included measures of verbal ability, visual and verbal memory, verbal fluency, working memory, executive functions and processing speed. Participants were classified in High or Low Positive Schizotypy (H-PST or L-PST), High or Low Paranoia-like traits (H-PAR or L-PAR) and High or Low Negative Schizotypy (H-NST or L-NST) groups, respectively. RESULTS: Individuals with H-PST performed significantly (p < 0.05) worse than L-PST on measures of processing speed and executive functions. Processing speed deficits were also observed in individuals with H-PAR compared to L-PAR (p < 0.05). There were no statistically significant differences in neuropsychological performance between H-NST and L-NST on any measure. CONCLUSIONS: In a population-based community sample, individuals with high positive schizotypal traits or paranoia-like traits show impairments in processing speed. Consistent with a dimensional view of psychosis, this supports the hypothesis that processing speed represents a core deficit of schizophrenia-like mental states.

Irrelevant features of a stimulus can either facilitate or disrupt performance in a working memory task: the role of fluid intelligence.

It has been shown that fluid intelligence (gf) is fundamental to overcome interference due to information of a previously encoded item along a task-relevant domain. However, the biasing effect of task-irrelevant dimensions is still unclear as well as its relation with gf. The present study aimed at clarifying these issues. Gf was assessed in 60 healthy subjects. In a different session, the same subjects performed two versions (letter-detection and spatial) of a three-back working memory task with a set of physically identical stimuli (letters) presented at different locations on the screen. In the letter-detection task, volunteers were asked to match stimuli on the basis of their identity whereas, in the spatial task, they were required to match items on their locations. Cross-domain bias was manipulated by pseudorandomly inserting a match between the current and the three back items on the irrelevant domain. Our findings showed that a task-irrelevant feature of a salient stimulus can actually bias the ongoing performance. We revealed that, at trials in which the current and the three-back items matched on the irrelevant domain, group accuracy was lower (interference). On the other hand, at trials in which the two items matched on both the relevant and irrelevant domains, the group showed an enhancement of the performance (facilitation). Furthermore, we demonstrated that individual differences in fluid intelligence covaries with the ability to override cross-domain interference in that higher gf subjects showed better performance at interference trials than low gf subjects. Altogether, our findings suggest that stimulus features irrelevant to the task can affect cognitive performance along the relevant domain and that gf plays an important role in protecting relevant memory contents from the hampering effect of such a bias.