前额叶损伤患者基于事件和基于时间的前瞻性记忆损害

目的探讨前额叶(PFC)损伤患者基于事件的前瞻性记忆(EBPM)和基于时间的前瞻性记忆(TBPM)的损害情况,验证PFC参与前瞻性记忆神经机制的假说。方法建立前瞻性记忆的神经心理学测验方法,测试年龄、教育程度相匹配的30名健康人和30例前额叶损伤患者的EBPM和TBPM。结果与健康对照组[EBPM(6.00±1.91)分;TBPM(5.30±0.92)分]相比,前额叶损伤组的EBPM[(1.47±1.07)分]差异有统计学意义(P<0.01),而TBPM[(4.77±1.17)分]的差异却无统计学意义(P>0.05)。左右侧PFC损伤组的EBPM[(1.40±1.12)、(1.64±1.01)分]和TBPM[(4.60±1.06)、(4.86±1.29)分]的差异均无统计学意义(P>0.05)。结论前额叶损伤患者的EBPM存在损害,而TBPM却相对正常,这说明EBPM和TBPM可能有着不同的脑机制。相对于TBPM,前额叶可能更多地参与了EBPM的认知加工。     

The hemodynamics of cognitive control: the level of concentration of oxygenated hemoglobin in the superior prefrontal cortex varies as a function of performance in a modified Stroop task

The purpose of this study was to establish the relationship between the hemodynamic response of prefrontal cortex (PFC) and individual differences in cognitive control, as measured by a color-word interference task. Twenty-five healthy volunteers were observed through functional near infrared spectroscopy (fNIRS) while performing a modified Stroop paradigm. Mean concentration levels of oxygenated hemoglobin (oxy-Hb) were correlated with behavioral performance in the conflict task. Those with shorter reaction times had higher levels of oxy-Hb concentration in superior dorsolateral PFC. Our results are the first to show a positive correlation between behavioral performance and oxy-Hb levels in superior dorsolateral PFC in a cognitive conflict task. These results suggest that the availability of oxygen in the superior PFC, possibly linked to an increase in metabolism, may be related to attention level and effectiveness of cognitive control.     

Differential activation of ventrolateral prefrontal cortex during working memory retrieval

Brain imaging studies have suggested a predominant involvement of prefrontal areas during retrieval of information from working memory (WM). This study used event-related functional magnetic resonance imaging to assess the gradual recruitment of brain areas during verbal WM-retrieval with a parametrically varied modified version of the Sternberg Item Recognition Paradigm. In particular, we were interested in activation differences during retrieval of negative and positive probes. Fifteen subjects performed a WM-task which required the retrieval of a probe letter from a set of a maximum of three letters. The analysis of the retrieval period regardless of probe type revealed bilateral VLPFC activation during retrieval from a single remembered item. These initially activated regions showed a gradual activation increase of left VLPFC (BA 47) and anterior PFC (BA 10) as well as and bilateral DLPFC (BA 9) with increasing retrieval demand, i.e. during retrieval of two and three previously remembered letters. The comparison of negative and positive probes (non-targets versus targets) revealed greater activity in VLPFC (BA 47) in response to negative than to positive probes. These findings demonstrate that ventral areas of prefrontal cortex seem to be differentially engaged during the discrimination of a non-target from a previously manipulated set.     

Deficits in prospective memory following damage to the prefrontal cortex

Neuropsychological investigations of prospective memory (PM), representing memory of future intentions or plans, have evolved over the past two decades. The broadly accepted divisions involved in PM consist of a prospective memory component (PMC), a process for remembering to remember, and a retrospective memory component, a process for remembering the content of the intended action. Previous functional neuroimaing studies have provided some evidence that the rostral prefrontal cortex (BA10) is one of areas that is critical for prospective remembering. However, the question of whether damage to part of the prefrontal cortex affects attenuated performance for PMC remains unresolved. In this study, 74 participants with traumatic brain injury (TBI) including focal damage to frontal or temporal lobe areas were administered thirteen standard neuropsychological tests and the PM task. To identify influential areas contributing to PM performance, discriminant function analysis was conducted. The results indicated that the following three areas are highly contributory to PM performance: the right dorsolateral prefrontal cortex; the right ventromedial prefrontal cortex; and the left dorsomedial prefrontal cortex. Comparing differences in neuropsychological test scores showed that orientation scores were significantly higher in the greater PM performance group, suggesting that PMC represents an integrated memory function associated with awareness of current status. These data contribute to our understanding of the neural substrates and functional characteristics of the PMC.     

Dissociable roles of prefrontal subregions in self-ordered working memory performance

The anatomical segregation of executive control processes within the prefrontal cortex remains poorly defined. The present study focused on strategy implementation on two working memory tasks: the CANTAB spatial working memory task and a visuospatial sequence generation task. These measures were administered to a group of frontal lesion patients and a comparison group of healthy subjects. Frontal patients with damage to the right inferior frontal gyrus were impaired on the CANTAB spatial working memory task, compared with healthy controls and patients without damage to this region. This deficit was most strongly related to the pars opercularis subregion (BA44) and was accompanied by poor strategy usage. On the sequence generation task, frontal lesion patients were impaired on a strategy-training phase when the working memory demands of the task were reduced, but had relatively intact performance on other phases of the task. Performance on the training phase was correlated with the amount of damage to the dorsolateral prefrontal cortex (DLPFC: BA46/9). These results support theoretical notions of prefrontal cortical function that emphasise its contribution to executive processes such as mnemonic strategies and monitoring over its role as a short-term memory store. Moreover, we provide evidence for the first time that such functions are dependent on dissociable brain regions within the prefrontal cortex.     

Proactive and reactive cognitive control rely on flexible use of the ventrolateral prefrontal cortex

The role of ventral versus dorsolateral prefrontal regions in instantiating proactive and reactive cognitive control remains actively debated, with few studies parsing cue versus probe‐related activity. Rapid sampling (460 ms), long cue–probe delays, and advanced analytic techniques (deconvolution) were therefore used to quantify the magnitude and variability of neural responses during the AX Continuous Performance Test (AX‐CPT; N = 46) in humans. Behavioral results indicated slower reaction times during reactive cognitive control (AY trials) in conjunction with decreased accuracy and increased variability for proactive cognitive control (BX trials). The anterior insula/ventrolateral prefrontal cortex (aI/VLPFC) was commonly activated across comparisons of both proactive and reactive cognitive control. In contrast, activity within the dorsomedial and dorsolateral prefrontal cortex was limited to reactive cognitive control. The instantiation of proactive cognitive control during the probe period was also associated with sparse neural activation relative to baseline, potentially as a result of the high degree of neural and behavioral variability observed across individuals. Specifically, the variability of the hemodynamic response function (HRF) within motor circuitry increased after the presentation of B relative to A cues (i.e., late in HRF) and persisted throughout the B probe period. Finally, increased activation of right aI/VLPFC during the cue period was associated with decreased motor circuit activity during BX probes, suggesting a possible role for the aI/VLPFC in proactive suppression of neural responses. Considered collectively, current results highlight the flexible role of the VLPFC in implementing cognitive control during the AX‐CPT task but suggest large individual differences in proactive cognitive control strategies.     

Sustained activation and executive control in the avian prefrontal cortex

We review our studies examining neural correlates of directed forgetting and executive control in the avian prefrontal cortex. One of the fundamental forms of executive control is the ability to selectively filter information, retaining that which is critical for the current purposes and discarding that which is not. In our first experiment, we trained birds on a directed-forgetting version of a delayed matching-to-sample task. Following a sample stimulus, a bird heard either a remember tone indicating that a memory test would follow, or a forget tone indicating that no memory test would be given. We found that neural activity in the avian prefrontal cortex increased when the bird was told to remember, and decreased when the bird was told to forget. Behavioral probe tests confirmed that the animals were forgetting on forget trials.Although the sustained activation observed on remember trials and the absence of such activation on forget trials could be a code of remembering and forgetting the sample stimulus, it could also be a code of the possibility of obtaining a reward. To address this issue we conducted a second study in which we used three cues: remember, forget, and forget–reward. The forget–reward cue instructed the subject to forget the sample yet at the same time provided a free reward. Neural activity on forget–reward trials matched that on remember trials tentatively indicating that the sustained activation on remember trials might be a reward code rather than a sample stimulus code. Behavioral probe tests, however, failed to indicate that the animals were forgetting on forget–reward trials, and hence it still is possible that the sustained activation could be a code for memory of the sample stimulus.     

Differentiation in prefrontal cortex recruitment during childhood: Evidence from cognitive control demands and social contexts

Emerging cognitive control during childhood is largely supported by the development of distributed neural networks in which the prefrontal cortex (PFC) is central. The present study used fNIRS to examine how PFC is recruited to support cognitive control in 5–6 and 8-9-year-old children, by (a) progressively increasing cognitive control demands within the same task, and (b) manipulating the social context in which the task was performed (neutral, cooperative, or competitive), a factor that has been shown to influence cognitive control. Activation increased more in left than right PFC with cognitive control demands, a pattern which was more pronounced in older than younger children. In addition, activation was higher in left PFC in competitive than cooperative contexts, and higher in right PFC in cooperative and neutral than competitive contexts. These findings suggest that increasingly efficient cognitive control during childhood is supported by more differentiated recruitment of PFC as a function of cognitive control demands with age.     

Semantic strategy training increases memory performance and brain activity in patients with prefrontal cortex lesions

Objective

Memory deficit is a frequent cognitive disorder following acquired prefrontal cortex lesions. In the present study, we investigated the brain correlates of a short semantic strategy training and memory performance of patients with distinct prefrontal cortex lesions using fMRI and cognitive tests.

Methods

Twenty-one adult patients with post-acute prefrontal cortex (PFC) lesions, twelve with left dorsolateral PFC (LPFC) and nine with bilateral orbitofrontal cortex (BOFC) were assessed before and after a short cognitive semantic training using a verbal memory encoding paradigm during scanning and neuropsychological tests outside the scanner.

Results

After the semantic strategy training both groups of patients showed significant behavioral improvement in verbal memory recall and use of semantic strategies. In the LPFC group, greater activity in left inferior and medial frontal gyrus, precentral gyrus and insula was found after training. For the BOFC group, a greater activation was found in the left parietal cortex, right cingulated and precuneus after training.

Conclusion

The activation of these specific areas in the memory and executive networks following cognitive training was associated to compensatory brain mechanisms and application of the semantic strategy.