Working Memory Accuracy Research Articles

The impact of affective information on working memory: A pair of meta-analytic reviews of behavioral and neuroimaging evidence.

Everyday life is defined by goal states that are continuously reprioritized based on available, often affective information. To pursue these goals, individuals need to process and maintain goal-relevant information, while ignoring potentially salient information that distracts resources from these goals. Empirically, this ability has typically been operationalized as working memory (WM) capacity. A growing body of research is investigating the impact of information’s affective salience on WM capacity. In the present review we address this question by exploring the potential differential impact of affective compared with neutral information on WM, and the underlying neural substrates. One-hundred and 65 studies (N = 7,433) were included in the meta-analysis. Results showed negligible to small (d̂ = −.07–.20) effects of affective information on behavioral measures of WM in healthy individuals (n = 4,936) that varied as a function of valence and task-relevance. Heterogeneity analyses were significant, demonstrating the need to identify further study-specific factors and individual differences that moderate affective WM. At the neural level (33 studies; n = 683), processing affective versus neutral material during WM tasks was associated with more frequent recruitment of the vlPFC, the amygdala, and the temporo-occipital cortex. In contrast to healthy individuals, across behavioral studies those suffering from mental health problems (n = 2,041) showed impaired WM accuracy (d̂ = −0.21) in the presence of affective material. These findings highlight the importance of integrating behavioral and neural levels of analysis. Finally, these findings suggest that affective WM capacity may be a transdiagnostic mechanism associated with poor mental health.

Assessing the Role of the Left Dorsal Frontal Cortex in Working Memory Guidance: Attentional or Mnemonic? A Neurostimulation Study

Perceptual selection can be guided by the contents of working memory (WM). Neuroimaging and neuropsychological data point to a role of a fronto-parietal and fronto-thalamic networks in WM guidance. Here we assessed the effect of transcranial direct current stimulation of the left dorsal frontal cortex (lDFC) in a combined WM/attention paradigm. We asked the extent to which the lDFC is implicated in mnemonic and selective attention functions during WM guidance of behavior. Observers were asked to keep information in memory while searching for a visual target, while the validity of WM contents for the search task varied. We tested the effects of lDFC-tDCS on the strength of WM guidance of search, whether any tDCS effect is dependent on the amount of WM load, and whether lDFC-tDCS primarily influences how WM contents are retained, the process of selective attention in search task, or both. Consistent with prior behavioral findings, we found that (i) selection of items that matched the contents of WM was facilitated relative to non-matching items and (ii) this WM guidance effect was reduced when the level processing/cognitive load in WM was higher. Notably, across two experiments we found that lDFC-tDCS modulated WM guidance of visual selection in the context of high processing loads in WM. No effects of tDCS were observed in WM accuracy. These findings suggest that the role of the left dorsal frontal cortex in WM guidance is associated with selective attentional control rather than mnemonic processing.

Anodal Transcranial Direct Current Stimulation Induces High Gamma-Band Activity in the Left Dorsolateral Prefrontal Cortex During a Working Memory Task: A Double-Blind, Randomized, Crossover Study.

Transcranial direct current stimulation (tDCS) has been shown to have mixed effects on working memory (WM) capacity in healthy individuals. Different stimulation paradigms may account for these discrepancies, with certain features being favored. To determine the effect in the context of anodal tDCS, we investigated whether anodal tDCS induced cortical oscillatory changes during a WM task. Specifically, we tested whether anodal offline tDCS over the left prefrontal cortex (PFC) enhances WM capacity by modulating the oscillatory activity in the left dorsolateral PFC (DLPFC) using magnetoencephalography (MEG). This study employed a double-blind, randomized, crossover design, in which 24 healthy right-handed participants conducted MEG recordings during a 3-back task after administration of 2 mA tDCS or sham stimulation as a placebo. Our results showed that the effect of tDCS did not appear in the behavioral indices—WM accuracy (d′) or reaction time (RT). From the results of the time-frequency analysis, significant event-related synchronization (ERS) in the high-gamma band (82–84 Hz) of the left DLPFC was found under the tDCS condition; however, ERS was not correlated with WM capacity. Furthermore, we calculated the modulation index (MI), which indicates the strength of phase-amplitude coupling (PAC). tDCS significantly decreased MI of the left DLPFC, representing the theta-gamma PAC during the n-back task using color names as verbal stimuli. Our results suggest that although tDCS increased the gamma-band oscillation indicating greater neural activity in the left DLPFC, it did not lead to an improvement of WM capacity; this may be due to the inability of gamma-band oscillation to couple with the task-induced theta wave. WM capacity might not increase unless theta-gamma PAC is not enhanced by tDCS.

Changes in Theta but not Alpha Modulation Are Associated with Impairment in Working Memory in Alzheimer's Disease and Mild Cognitive Impairment.

While several studies have found that neural oscillations play a key role in the functioning of working memory, the nature of aberrant oscillatory activity underlying working memory impairments in Alzheimer's disease (AD) and mild cognitive impairment (MCI) remains largely unexplored. These individuals often display structural alterations in brain regions and pathways involved in working memory processes and therefore may also display altered oscillatory activity during memory activation. Electroencephalographic (EEG) activity was recorded during the N-back working memory task in three groups: AD (n = 29), MCI (n = 100), and healthy controls (HCs; n = 40). Theta (4-7 Hz) and alpha (7.5-12 Hz) modulation was measured in response to the stimulus presentation during correct and incorrect responses. This modulation represents the change in EEG activity associated with the stimulus onset and was measured as a ratio of post stimulus power to pre stimulus power. We also assessed the relationship between change in oscillatory power and working memory performance. Compared to HCs, the AD group demonstrated the lowest working memory accuracy and a smaller theta ratio for correct responses on the 2-back condition; the MCI group demonstrated a smaller theta ratio for correct responses on the 3-back condition. Finally, we observed that the theta ratio, but not the alpha ratio, was a significant predictor of working memory performance in the three groups for all conditions. Taken together, these behavioral and electrophysiological results suggest that in addition to impairments in working memory performance, modulation of theta, but not alpha power, may be impaired in MCI and AD.

Stimuli may have little impact on the deficit of visual working memory accuracy in first-episode schizophrenia.

PurposeWorking memory (WM) deficits have been observed in people with schizophrenia (SZ) and are considered a core cognitive dysfunction in these patients. However, little is known about how stimuli and memory load influence visual WM deficits.Patients and methodsIn the present study, we adopted a match-to-sample task to examine the visual WM in 18 first-episode patients with SZ and 18 healthy controls (HCs). Faces and houses were used as the stimuli, and there were two levels of memory load – one item and two items; the average accuracy (ACC) and reaction time were calculated for each condition. The Positive and Negative Syndrome Scale and the Personal and Social Performance scale were used to assess the psychiatric symptoms and social function, respectively.ResultsThe results showed equivalent levels of WM deficit when using face and house stimuli. Moreover, the WM deficits were not related to the duration of illness, medication, or SZ symptoms.ConclusionThese results demonstrate that stimuli may have little impact on ACC in WM tasks in people with SZ. In addition, the memory load may have little impact on WM ACC when the load is relatively low.

Enhancing effects of acute exposure to cannabis smoke on working memory performance.

Numerous preclinical studies show that acute cannabinoid administration impairs cognitive performance. Almost all of this research has employed cannabinoid injections, however, whereas smoking is the preferred route of cannabis administration in humans. The goal of these experiments was to systematically determine how acute exposure to cannabis smoke affects working memory performance in a rat model. Adult male (n = 15) and female (n = 16) Long-Evans rats were trained in a food-motivated delayed response working memory task. Prior to test sessions, rats were exposed to smoke generated by burning different numbers of cannabis or placebo cigarettes, using a within-subjects design. Exposure to cannabis smoke had no effect on male rats' performance, but surprisingly, enhanced working memory accuracy in females, which tended to perform less accurately than males under baseline conditions. In addition, cannabis smoke enhanced working memory accuracy in a subgroup of male rats that performed comparably to the worst-performing females. Exposure to placebo smoke had no effect on performance, suggesting that the cannabinoid content of cannabis smoke was critical for its effects on working memory. Follow-up experiments showed that acute administration of either Δ9-tetrahydrocannabinol (0.0, 0.3, 1.0, 3.0 mg/kg) or the cannabinoid receptor type 1 antagonist rimonabant (0.0, 0.2, 0.6, 2.0 mg/kg) impaired working memory performance. These results indicate that differences in the route, timing, or dose of cannabinoid administration can yield distinct cognitive outcomes, and highlight the need for further investigation of this topic.

Analysis of influencing factors of visual working memory in young adult patients with schizophrenia

BackgroundPatients with schizophrenia have general cognitive impairments, and the impairment of working memory is considered to be the basis of cognitive impairments. The research on visual working memory, one of...

Retroactive Attentional Shifts Predict Performance in a Working Memory Task: Evidence by Lateralized EEG Patterns.

Shifts of attention within working memory based on retroactive (retro-) cues were shown to facilitate performance in working memory tasks. Although posterior asymmetries in the EEG, such as the contralateral delay activity (CDA), have been used to study the active storage of lateralized working memory representations, results on the relation of such asymmetric effects to retro-cue benefits remain inconclusive. We recorded EEG in a retro-cue working memory task with lateralized items and a continuous performance response. Following either a selective or neutral retro-cue, participants adjusted the orientation of a central memory probe to the cued item. Selective retro-cues elicited an early posterior contralateral negativity (PCN), anterior directing attention negativity (ADAN) and a later modulation of CDA indicating that active storage was concentrated on the cued information. By dividing all trials into three within-condition performance quantiles, we could further show that high working memory accuracy was associated with a sustained increase of the CDA effect following the retro-cue. These results suggest that focusing resources on the active storage of relevant representations is an important factor regarding retro-cue benefits in working memory tasks.

Somatostatin Interneurons Facilitate Hippocampal-Prefrontal Synchrony and Prefrontal Spatial Encoding

Decreased hippocampal-prefrontal synchrony may mediate cognitive deficits in schizophrenia, but it remains unclear which cells orchestrate this long-rangesynchrony. Parvalbumin (PV)- and somatostatin (SOM)-expressing interneurons show histological abnormalities in individuals with schizophrenia and are hypothesized to regulate oscillatory synchrony within the prefrontal cortex. To examine the relationship between interneuron function, long-range hippocampal-prefrontal synchrony, and cognition, we optogenetically inhibited SOM and PV neurons in the medial prefrontal cortex (mPFC) of mice performing a spatial working memory task while simultaneously recording neural activity in the mPFC and the hippocampus (HPC). We found that inhibiting SOM, but not PV, interneurons during the encoding phase of the task impaired working memory accuracy. This behavioral impairment was associated with decreased hippocampal-prefrontal synchrony and impaired spatial encoding in mPFC neurons. These findings suggest that interneuron dysfunction may contribute to cognitive deficits associated with schizophrenia by disrupting long-range synchrony between the HPC and PFC.

Beneficial effects of anodal transcranial direct current stimulation (tDCS) on spatial working memory in patients with schizophrenia

Schizophrenia is a severe and often detrimental psychiatric disorder. The individual patients’ level of functioning is essentially determined by cognitive, particularly working memory (WM), deficits that are critically linked to dysfunctional activity of the dorsolateral prefrontal cortex (dlPFC). Transcranial direct current stimulation (tDCS) can transiently modulate activity of the dlPFC and remote areas and has been shown to improve WM functions. It may therefore provide a new, targeted treatment option.For this aim, the present study investigated the effect of anodal tDCS of different intensities on spatial WM in patients with schizophrenia. In two experiments, 32 patients performed a spatial n-back task with increasing WM load (1-, 2-, and 3-back) at baseline and in two sessions with anodal or sham tDCS (EXP I [n = 16]: 1 mA; EXP II [n = 16]: 2 mA) to the right dlPFC (cathode: left m. deltoideus). With 1 mA anodal tDCS, no effect on WM performance could be detected. However, 2 mA anodal tDCS increased accuracy (measured by d’) of the task with the highest WM load (3-back). This effect was larger in patients with a lower level of general neurocognitive functioning.These results demonstrate a beneficial effect of 2 mA anodal tDCS on deficient WM accuracy in patients with schizophrenia particularly under challenging conditions and in subjects with higher cognitive impairments. This data will inform future clinical trials on tDCS-enhanced cognitive training to improve treatment of schizophrenia.

The Sources of Dual-task Costs in Multisensory Working Memory Tasks.

We investigated the sources of dual-task costs arising in multisensory working memory (WM) tasks, where stimuli from different modalities have to be simultaneously maintained. Performance decrements relative to unimodal single-task baselines have been attributed to a modality-unspecific central WM store, but such costs could also reflect increased demands on central executive processes involved in dual-task coordination. To compare these hypotheses, we asked participants to maintain two, three, or four visual items. Unimodal trials, where only this visual task was performed, and bimodal trials, where a concurrent tactile WM task required the additional maintenance of two tactile items, were randomly intermixed. We measured the visual and tactile contralateral delay activity (CDA/tCDA components) as markers of WM maintenance in visual and somatosensory areas. There were reliable dual-task costs, as visual CDA components were reduced in size and visual WM accuracy was impaired on bimodal relative to unimodal trials. However, these costs did not depend on visual load, which caused identical CDA modulations in unimodal and bimodal trials, suggesting that memorizing tactile items did not reduce the number of visual items that could be maintained. Visual load did not also affect tCDA amplitudes. These findings indicate that bimodal dual-task costs do not result from a competition between multisensory items for shared storage capacity. Instead, these costs reflect generic limitations of executive control mechanisms that coordinate multiple cognitive processes in dual tasks. Our results support hierarchical models of WM, where distributed maintenance processes with modality-specific capacity limitations are controlled by a central executive mechanism.

Differential effects of high-definition transcranial direct current stimulation on verbal working memory performance according to sensory modality

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that modulates cortical excitability in a polarity-dependent manner. The diffuse nature of tDCS makes it difficult to investigate the optimal stimulation parameters for more effective and specific cognitive enhancement; to address this deficit, a more focalized stimulation technique, high-definition tDCS (HD-tDCS), has been developed. To date, only a few studies have examined the effects of HD-tDCS on cognitive functions; and none has investigated the effects of HD-tDCS on different sensory modalities of verbal working memory. Therefore, the present study compared the effects of prefrontal HD-tDCS on visual and auditory working memory tasks. Twenty healthy participants completed three sessions of each modality task, and additionally a sustained attention task. Anodal or sham HD-tDCS was administered to the dorsolateral prefrontal cortex (DLPFC) during the second session of the task in a parallel, single-blind design. Anodal stimulation to the DLPFC significantly enhanced the visual verbal working memory accuracy during and 20 min after the stimulation. In contrast, auditory verbal working memory performance was not modulated by anodal stimulation. Anodal stimulation to the DLPFC showed no effect on any other cognitive functions. The present study revealed the differential effects of HD-tDCS on two different modalities (visual vs. auditory) of working memory performance: important preliminary findings for the establishment of a more effective and specific use of tDCS.

Effect of sleep deprivation on emotional working memory.

The emotional dysregulation and impaired working memory found after sleep loss can have severe implications for our daily functioning. Considering the intertwined relationship between emotion and cognition in stimuli processing, there could be further implications of sleep deprivation in high‐complex emotional situations. Although studied separately, this interaction between emotion and cognitive processes has been neglected in sleep research. The aim of the present study was to investigate the effect of 1 night of sleep deprivation on emotional working memory. Sixty‐one healthy participants (mean age: 23.4 years) were either sleep deprived for 1 night (n = 30) or had a normal night’s sleep (n = 31). They performed an N‐back task with two levels of working memory load (1‐back and 3‐back) using positive, neutral and negative picture scenes. Sleep deprivation, compared with full night sleep, impaired emotional working memory accuracy, but not reaction times. The sleep‐deprived participants, but not the controls, responded faster to positive than to negative and neutral pictures. The effect of sleep deprivation was similar for both high and low working memory loads. The results showed that although detrimental in terms of accuracy, sleep deprivation did not impair working memory speed. In fact, our findings indicate that positive stimuli may facilitate working memory processing speed after sleep deprivation.

No Evidence That Baseline Prefrontal Cortical Excitability (3T-MRS) Predicts the Effects of Prefrontal tDCS on WM Performance.

Transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (lDLPFC) is a promising tool to enhance working memory (WM) in clinical as well as healthy populations. Yet, tDCS does not affect everyone similarly: whereas tDCS improves WM in most individuals, some individuals do not, or actually show detriments in WM performance after stimulation. One hypothesis that has been put forward to account for individual differences in tDCS response is that baseline cortical excitability levels in the stimulated cortex may determine the strength and the direction of the effects of tDCS. Specifically, by locally affecting neuronal excitability, tDCS may interact with baseline cortical excitability levels, thereby pushing or pulling individuals toward or away from an optimal level of cortical functioning. In the current study, we put this hypothesis to the test with regard to prefrontal cortex stimulation and WM. In 20 healthy male participants, using magnetic resonance spectroscopy (MRS) at 3T, we measured concentrations of Glutamate and GABA in the lDLPFC and calculated individual Glutamate/GABA ratios as a measure for cortical excitability. Subsequently, in two stimulation sessions, we once applied anodal and once cathodal tDCS over the lDLPFC (20 min, 1 mA). Stimulation was always applied in the second block of three blocks of a WM updating task. Surprisingly, at the group-level, we found no effects of anodal or cathodal stimulation on WM performance. Yet, in line with previous studies, large individual variability was observed in the strength and direction of tDCS effects; whereas about half of the participants improved, the other half showed lower accuracy after stimulation. This was true for both anodal and cathodal tDCS. Nevertheless, contrary to our expectations, individual baseline prefrontal cortical excitability did not predict these individual differences in the effect of anodal or cathodal stimulation on WM accuracy. Future studies with larger sample sizes, which use higher magnetic field strengths (e.g., 7T) to measure cortical excitability and/or apply individualized stimulation protocols, are necessary to shed more light on the influence of baseline cortical excitability on effects of anodal and cathodal tDCS over lDLPFC on WM performance.

The cost of facing fear: Visual working memory is impaired for faces expressing fear.

Previous research has identified numerous factors affecting the capacity and accuracy of visual working memory (VWM). One potentially important factor is the emotionality of the stimuli to be encoded and held in VWM. We often must hold in VWM information that is emotionally charged, but much is still unknown about how the emotionality of stimuli impacts VWM performance. In the current research, we performed four studies examining the impact of fearful facial expressions on VWM for faces. Fearful expressions were found to produce a consistent cost to VWM performance. This cost was modulated by encoding time, but not set size. This cost was only present for faces in an upright orientation consistent with this cost being a product of the emotionality of the faces rather than lower-level perceptual differences between neutral and fearful faces. These findings are discussed in the context of existing theoretical accounts of the impact of emotion on information processing. We suggest that a number of competing effects drive both costs and benefits and are at play when emotional information must be stored in VWM, with the task context determining the balance between them.

P34. Working memory for faces in congenital prosopagnosia: altered neural representations in the fusiform face area

Background Face recognition is a key skill of social cognition. Congenital prosopagnosia (CP), i.e. the inability to recognize faces in the absence of any other underlying pathology, is a model system for the understanding of face processing and affects about 2% of the population. Controversy exists whether activation of the fusiform face area (FFA), a core region within the face processing network, is preserved in CP. Here we scrutinized the global activity of the FFA in a working memory paradigm and specifically probed neural representations with Representational Similarity Analysis (RSA). Methods A total of 13 CP and 12 healthy control participants were included. Diagnosis was based on a semi-structured interview (Kennerknecht et al., 2008). CP subjects showed poorer performance in the Cambridge Face Memory Test (Duchaine et al., 2006), an independent diagnostic tool for CP. A modified Sternberg working memory paradigm presented faces with three levels of difficulty: low load condition (1 face, 3 scrambled pictures), medium load condition (2 faces, 2 scrambled pictures), and high load memory condition (4 faces). After a maintenance phase, a probe picture was shown. Working memory processing in the right fusiform face area (FFA), individually determined by a functional localizer, was analyzed with a modified RSA approach (Kriegeskorte et al., 2008). RSA assesses the correlation of voxel-wise activity across trials, represented in individual correlation matrices. Mean correlation coefficients were computed for each condition across groups and a group comparison of individual correlation matrices was performed with a random walk mapping and Donsker’s theorem (Donsker, 1951). Results CP participants showed significantly lower working memory accuracy, most notably in the high load condition. For FFA activation in the encoding phase, an ANOVA yielded a significant effect of group (F = 5.82, p = 0.024), and condition (low, medium, high memory load) (F = 38.02, p 0.001 ). When comparing mean correlation coefficients of the RSA in an ANOVA, we found an effect of condition ( p 0.001 ) and a trend for the factor group (p = 0.058) with CP participants showing lower mean correlation of voxel activity as compared to control participants. Individual matrix comparison based on Donsker’s theorem allowed to confirm the group difference in all memory load conditions. Conclusion Our study on working memory processing in CP revealed both a global reduction of FFA activity and altered neural representations as assessed by representational similarity analysis. We suggest that the latter effect contributes to deficits in face recognition.

Improving working memory in schizophrenia: Effects of 1 mA and 2 mA transcranial direct current stimulation to the left DLPFC

Deficits in various cognitive processes, such as working memory, are characteristic for schizophrenia, lowering patients' functioning and quality of life. Recent research suggests that transcranial direct stimulation (tDCS) applied to the dorsolateral prefrontal cortex (DLPFC) may be a potential therapeutic intervention for cognitive deficits in schizophrenia. Here, we examined the effects of online tDCS to the DLPFC on working memory (WM) performance in 40 schizophrenia patients in two separate experiments with a double blind, sham-controlled, cross-over design. Patients underwent single sessions of active and sham tDCS in a randomized order. Stimulation parameters were anode F3, cathode right deltoid muscle, 21 min tDCS duration, 1 mA tDCS in Experiment 1 (N = 20) and 2 mA tDCS in Experiment 2 (N = 20). Primary outcome was the change in WM performance as measured by a verbal n-back paradigm (1- to 3-back). Irrespective of the stimulation intensity, data analysis showed a significant higher WM accuracy during active tDCS than during sham tDCS (p = 0.019), but no main effect of stimulation intensity (p = 0.392). Subsequent separate analyses revealed a significantly improved WM performance only during 1 mA (p = 0.048). TDCS facilitated WM functioning in schizophrenia, with an advantage of 1 mA over 2 mA. Our results support the notion that tDCS may be a potential treatment for cognitive deficits in schizophrenia and emphasize the need for future research on the specific stimulation parameters.

Effects of 2-day calorie restriction on cardiovascular autonomic response, mood, and cognitive and motor functions in obese young adult women.

Although long-term energy restriction has been widely investigated and has consistently induced improvements in health and cognitive and motor functions, the responses to short-duration calorie restriction are not completely understood. The purpose of this study was to investigate the effects of a 2-day very low-calorie diet on evoked stress, mood, and cognitive and motor functions in obese women. Nine obese women (body fatness > 32%) aged 22-31years were tested under two randomly allocated conditions: 2-day very low-calorie diet (511kcal) and 2-day usual diet. The perceived stressfulness of the diet, cardiovascular autonomic response, and cognitive and motor performances were evaluated before and after each diet. The subjective stress rating of the calorie-restricted diet was 41.5 ± 23.3. Calorie restriction had no detectable effects on the heart rate variability indices, mood, grip strength, or psychomotor functions. By contrast, calorie restriction increased (p < 0.05) spatial processing and visuospatial working memory accuracy, and decreased (p < 0.05) accuracy of cognitive flexibility. In conclusion, our results demonstrate that although a 2-day calorie restriction evoked moderate stress in obese women, cardiovascular autonomic function was not affected. Calorie restriction had complex effects on cognition: it declined cognitive flexibility, and improved spatial processing and visuospatial working memory, but did not affect mood or motor behavior.

Microstructural Changes in Higher-Order Nuclei of the Thalamus in Patients With First-Episode Psychosis

BackgroundDisruption in the thalamus, such as volume, shape, and cortical connectivity, is regarded as an important pathophysiological mechanism in schizophrenia. However, there is little evidence of nuclei-specific structural alterations in the thalamus during early-stage psychosis, mainly because of the methodological limitations of conventional structural imaging in identifying the thalamic nuclei. MethodsA total of 37 patients with first-episode psychosis and 36 matched healthy control subjects underwent diffusion tensor imaging, diffusion kurtosis imaging, and T1-weighted magnetic resonance imaging. Connectivity-based segmentation of the thalamus was performed using diffusion tensor imaging, and averages of the diffusion kurtosis values, which represent microstructural complexity, were estimated using diffusion kurtosis imaging and were compared in each thalamic nucleus between the groups. ResultsThe mean kurtosis values in the thalamic regions with strong connections to the orbitofrontal cortex (F1,70 = 8.40, p < .01) and the lateral temporal cortex (F1,70 = 8.46, p < .01) were significantly reduced in patients with first-episode psychosis compared with those of the healthy control subjects. The mean kurtosis values in the thalamic region with strong connection to the orbitofrontal cortex showed a significant correlation with spatial working memory accuracy in patients with first-episode psychosis (r = .36, p < .05), whereas no significant correlation between these variables was observed in the healthy control subjects. ConclusionsThe observed pattern of reduced microstructural complexity in the nuclei not only highlights the involvement of the thalamus but also emphasizes the role of the higher-order nuclei in the pathophysiology beginning in the early stage of schizophrenia.

Khat distorts the prefrontal cortex histology and function of adult Wistar rats

Khat is a psychoactive herbal drug of pronounced ethno-pharmacological significance often abused due to its unregulated use. It affects many brain centers including the prefrontal cortex which is the anterior most part of the frontal lobe. The prefrontal cortex modulates working memory, planning complex cognitive behaviors however; it is linked to many psychological disorders such as depression, schizophrenia and memory loss. We studied the effects exerted by khat on the PFC cytoarchitecture and functions since this part of the brain is highly interconnected with various cortical regions. This was an experimental study of 6 weeks. A total of 24 male adult wistar rats of 130g-155g were divided into four groups of 6 animals that received respective khat doses of 2000mg/kg, 1000mg/kg, 500mg/kg and 10ml/kg of distilled water for the controls. Brain to body weight ratio was determined at week 6 using an analytical balance (Fisher Science Education™, RS232C; USA). Histology of the brain was determined using H and E and Kulvers staining technique. Khat exhibited features of prefrontal cortex disorientation such as necrosis, vacuolations, chromatolysis, demyelination, cortical degeneration and hemorrhage in a dose dependent manner. Selective attention and working memory were impaired well as brain to body weight ratio was reduced significantly (P ≤ 0.05). Repeated exposure to khat distorts the prefrontal cortex cytoarchitecture and impairs selective attention and working memory accuracy due to ischemia and cell exhaustion by khat toxicity.Keywords: Khat, prefrontal cortex histology, working memory, selective attention