轻度认知损害和阿尔茨海默病的大脑灰质体积及其与记忆功能的关系

目的考察轻度认知损害(mild cognitive impairment,MCI)和阿尔茨海默病(Alzheimer’s disease,AD)的大脑灰质体积是否存在异常及其与记忆功能的关系。方法本研究共纳入56例轻度AD、14例MCI和16例正常对照,所有被试均进行了记忆功能测查和磁共振影像检查。影像数据分析采用患者基于体素的脑形态学分析(voxel-based morphometry,VBM)。结果 AD组和MCI组记忆测验评分下降,呈AD组相似文献   

轻度认知障碍工作记忆的fMRI研究

目的 :运用血氧水平依赖 (bloodoxygenationleveldependent ,BOLD)法功能磁共振成像 (functionalmagneticresonanceimaging ,fMRI)对轻度认知障碍 (mildcognitiveimpairment ,MCI)与正常对照组在记忆的激活区域范围及强度方面进行比较。方法 :对 6例MCI患者 ,8例认知正常老人进行神经心理学测试 ,在 1 5TPick磁共振扫描仪上进行记忆过程中的EPI序列的扫描 ,并运用相关软件分析所得图像及数据。结果 :MCI患者在颞叶激活范围比正常对照组小 ,时间 信号强度变化曲线亦有差异 ,右侧颞叶激活的范围和强度均高于左侧。结论 :MCI患者的记忆功能下降在fMRI上主要表现为颞叶激活范围的变化及激活强度的下降 ,颞叶可能是MCI记忆功能下降反应比较敏感的区域。     

2型糖尿病合并轻度认知损害的正电子发射计算机断层扫描研究

目的 探讨2型糖尿病(DM)合并轻度认知损害( MCI)患者脑葡萄糖代谢特点.方法 应用18-氟代脱氧葡萄糖(18F-FDG)正电子发射计算机断层扫描(PET),对7例单纯DM患者(DM组)、6例DM合并MCI患者(DM+ MCI组)及10名正常对照者(对照组)脑葡萄糖代谢进行检测；采用简易精神状态检查量表(MMSE)、画钟试验(CDT)及临床痴呆评定量表(CDR)测定患者认知功能.结果 (1)认知功能:DM+ MCI组的MMSE得分[(24.67±0.82)分]显著低于对照组[(29.20± 0.79)分]及DM组(29.14±1.21)分](P均＜0.01),CDR得分[(0.58±0.20)分]显著高于对照组[(0.10±0.21)分]及DM组[(0.14±0.24)分](P均＜0.01),CDT得分与对照组及DM组间差异无统计学意义.(2)18F-FDG PET检查:与对照组比较,DM组左顶叶平均标准化摄取值(SUV)半定量比值降低(1.03 ±0.07比1.16 ±0.09,P＜0.05),DM+ MCI组左额叶(1.02±0.16比1.15 ±0.08)、右额叶(0.90±0.07比1.10±0.06)、扣带回(0.92 ±0.06比1.17±0.08)、左顶叶(0.94±0.12比1.16±0.09)、右顶叶(0.93 ±0.10比1.11 ±0.06)、左颞顶后叶(0.96±0.11比1.17 ±0.01)、右颞顶后叶(0.90±0.09比1.15 ±0.06)的SUV半定量比值均降低(P＜0.01)；与DM组比较,DM+ MCI组左额叶(1.02±0.16比1.15 ±0.11)、右额叶(0.90±0.07比1.06±0.18)、扣带回(0.92 ±0.06比1.16± 0.08)、右顶叶(0.93±0.10比1.10±0.12)、左颞顶后叶(0.96±0.11比1.14 ±0.14)、右颞顶后叶(0.90±0.09比1.18±0.17)的SUV半定量比值降低(P＜0.01或P＜0.05).结论 2型糖尿病合并MCI患者的双侧额叶、扣带回、顶叶、颞顶后叶等多个脑区葡萄糖代谢均降低.     

戒断期海洛因依赖者额叶认知功能的功能磁共振成像研究

目的 研究戒断期海洛因依赖者(AHD)的脑认知功能.方法 采用3.0 T磁共振成像系统,对30例AHD(AHD组)和18名健康对照者(对照组)在完成Go/NoGo任务时行全脑功能磁共振成像(fMRI)扫描,记录反应时间(RT).结果 (1)RT:AHD组在完成Go/NoGo任务时的RT[(394±34)ms]长于对照组[(374±26)ms;P<0.05].(2)fMRI:对照组在完成Go/NoGo任务时,诱发激活双侧前额叶内侧回、前扣带回以及双侧额下回等脑区;AHD组全脑活动普遍低,仅有双侧额上回和左侧额中回激活.两组间比较,AHD组激活显著低于对照组的区域主要位于在双侧额内侧回、前扣带回、额下回及双侧颞叶等脑区(P<0.005).结论 戒断期海洛因依赖者反应抑制功能障碍仍然存在,促进其认知功能的恢复可能成为戒毒、抗复吸的有效策略.     

不同发作类型内侧颞叶癫灰质改变的结构性磁共振成像研究

目的探讨不同发作类型内侧颞叶癫患者灰质体积变化及其与病程的相关性。方法共40例内侧颞叶癫患者[部分性发作20例(m TLE-PS组)和继发性全面性发作20例(m TLE-s GS组)]以及20例性别、年龄相匹配的正常对照者行头部T1-三维磁化准备快速梯度回波扫描,采用基于体素的形态学分析进行灰质结构分割,选取双侧额叶和丘脑作为兴趣区,比较3组受试者各脑区灰质体积,采用Spearman秩相关分析探讨内侧颞叶癫患者各脑区灰质体积与病程的相关性。结果 3组受试者双侧额上回、右侧额中回、右侧额内侧回、右侧角回、右侧颞中回、右侧海马、双侧丘脑和双侧小脑半球灰质体积差异有统计学意义(均P0.01,FWE校正),与正常对照组相比,m TLE-PS组双侧额上回、小脑半球和右侧颞中回、海马、丘脑灰质体积减少(均P0.01,FWE校正),m TLE-s GS组双侧额上回、丘脑、小脑半球和右侧角回、颞中回、海马灰质体积减少(均P0.01,FWE校正);与m TLE-PS组相比,m TLE-s GS组双侧额上回、丘脑和右侧额内侧回、直回灰质体积减少(均P0.01,FWE校正)。m TLE-s GS组患者左侧额上回(rs=-0.611,P=0.004)和右侧额中回(rs=-0.562,P=0.010)与病程呈负相关关系。结论不同发作类型内侧颞叶癫患者均存在双侧额叶、丘脑、小脑半球和右侧颞叶、海马灰质损伤,但损伤脑区有所不同,继发性全面性发作患者以双侧额叶和丘脑灰质体积减少为主,提示丘脑-皮质环路是内侧颞叶癫继发性全面性发作的重要结构基础。     

轻度认知功能障碍患者正电子发射计算机体层摄影术和神经心理学测定的初步研究

目的　探讨轻度认知功能障碍患者脑葡萄糖代谢与神经心理学特点及其相互关系。方法　采用正电子发射体层摄影术 (PET)、简易智能状态测定 (MMSE)、韦克斯勒记忆量表测定 (WMS)和总体衰退量表 (GDS)测定 10例轻度认知功能障碍 (MCI)患者和 10名健康志愿者 (HC)。结果 (1)MCI组MMSE[(2 4.6± 2 2 )分 ]、WMS[(6 9.4± 10 .4)分 ]分值低于HC组 [分别为 (2 8.9± 1.1)分和 (93.1± 9.0 )分 ;P〈0 .0 1];(2 )MCI组左侧眶回、右侧颞叶中回和右侧壳核的局部脑葡萄糖代谢率 (rCMRglc)较HC组低 (P〈0 .0 5～ 0 .0 1) ;(3)将年龄、受教育年限、MMSE、WMS与不同脑区用18F标记的脱氧葡萄糖放射性比值进行相关分析显示 ,与年龄呈负相关 (P〈0 .0 5或P〈0 .0 1)的脑区有 :眶回、左侧额上回、左侧额下回、颞叶中回、颞叶下回、左侧顶叶、左侧中央前回、右侧中央后回、左颞叶内侧皮质、左侧海马回、左侧海马旁回、右侧前扣带回、后扣带回、左侧杏仁核等。与文化程度呈正相关 (P〈0 .0 5或P〈0 .0 1)的脑区有 :左侧颞叶下回、中央前回、左侧中央后回等 ;而右侧壳核则呈负相关。与MMSE呈正相关 (P〈0 .0 5或P〈0 .0 1)的脑区有 :额下回、左侧颞叶上回、颞叶中回、颞叶下回、左侧顶叶、左侧中央前回、中央后回、颞叶内侧皮     

轻型颅脑损伤静息态脑网络变化的研究

目的通过对轻型颅脑损伤病人进行静息态功能磁共振检查并采用低频振幅的方法进行数据分析,观察其脑网络异常激活区域。方法收集16例轻型颅脑损伤病人作为轻型颅脑损伤组,同时将23例正常志愿者作为正常对照组。采用低频振幅分析方法对两组进行静息态功能磁共振数据分析。结果与正常对照组比较,轻型颅脑损伤组脑网络出现6个异常激活脑区,主要分布于胼胝体前部、右侧额叶的前部及后部皮质、右侧顶枕联合皮质、左侧小脑半球底部、右侧枕极、双侧颞叶底部、双侧颞中回后部、双侧颞枕联合皮质及双侧额叶前部内侧皮质。结论轻型颅脑损伤病人静息态脑网络存在异常激活区域,静息态功能磁共振可能成为临床治疗中的重要诊断方法。     

颞叶癫痫对前瞻性记忆的影响

目的 探讨颞叶癫痫对基于事件的前瞻性记忆(event-based prospective memory,EBPM)和基于时间的前瞻性记忆(time-based prospective memory,TBPM)的影响,验证颞叶参与前瞻性记忆的神经机制假说.方法 采用McDaniel等建立的前瞻性记忆神经心理学试验方法,测试62例颞叶癫痫患者(33例服用抗癫痫药物和29例未服用药物,颞叶癫痫组)和年龄、教育程度相匹配的30名健康者(健康对照组)的EBPM和TBPM.结果 颞叶癫痫组简易精神状态检查(MMSE)、数字广度测试(DS)、词汇流畅性测试(VFT)的成绩均低于健康对照组,且MMSE、VFT两组间差异有统计学意义.与健康对照组[ EBPM测试(6.83±1.34)分,TBPM测试(5.00±1.70)分]相比,颢叶癫痫组的EBPM测试[(3.95±2.77)分]和TBPM测试[(3.08±2.42)分]的成绩差异均有统计学意义(t=6.72、4.39,均P＜0.01),且TBPM测试得分均低于EBPM.其中服药和未服药两组间EBPM测试成绩[(3.82±2 70)、(4.10±2.90)分]差异无统计学意义(t=-0.40,P ＞0.05),两组间TBPM测试成绩[(2.55±2.20)、(3.69±2.55)分]差异亦无统计学意义(t=-1.90,P＞0.05).结论 颞叶癫痫患者存在前瞻性记忆损害,提示颞叶参与前瞻性记忆的神经机制过程;与EBPM相比,TBPM损害更明显,提示TBPM需要更多的自我发动过程.     

不同亚型轻度认知功能损害患者的神经心理学特征

目的 探讨不同亚型轻度认知功能损害(MCI)患者的神经心理学特征.方法 采用多种神经心理学量表对28例遗忘型MCI (aMCI)、21例血管型MCI (V-MCI)、21例帕金森病型MCI(PD-MCI)及46名健康老年人进行评定,比较不同亚型MCI的神经心理学特征.结果 (1)与健康对照组比较,各亚型MCI组在总体认知评分及剑桥老年认知检查量表中文版(CAMCOG-C)子项评分差异均有统计学意义.aMCI组在定向、语言表达、近记忆、学习记忆、注意、计算、思维及知觉方面均受损,差异具有统计学意义(t=4.580、5.150、3.053、4.070、5.918、2.121、2.952、3.175,均P＜0.05);语言理解、远记忆与执行能力相对保留,差异无统计学意义.V-MCI组定向、语言表达、注意与执行功能受损(t=2.974、3.165、4.216、3.197,均P＜0.05),记忆力、计算、思维及知觉较对照组差异无统计学意义.PD-MCI组在语言表达、近记忆、远记忆、学习记忆、注意及执行功能方面损害均显著,差异具有统计学意义(t=4.433、3.065、3.821、3.447、5.344、0.348,均P＜0.05).(2)各亚型MCI组间比较:与V-MCI组[(3.52±0.87)分、(12.48±1.83)分]相比,aMCI组[(3.07±0.81)分、(11.07±2.28)分]与PD-MCI组[(3.00 ±0.89)分、(11.33 ±1.91)分]在CAMCOG-C总体评分及其子项中记忆能力包括近记忆、学习记忆降低显著,差异具有统计学意义(aMCI与V-MCI比较t=1.868、2.381,PD-MCI与V-MCI比较t=1.921、1.980;均P＜0.05).PD-MCI组中,远记忆及执行功能较其他两组显著降低,差异具有统计学意义(与aMCI比较t=2.498、4.257,与V-MCI比较t=1.684、1.492:均P＜0.05).(3)aMCI组GDS评分较健康对照组显著增高,差异具有统计学意义(t=2.850,P＜0.05),而V-MCI组及PD-MCI组与健康对照组比较差异均无统计学意义,但aMCI组及V-MCI组GDS得分较PD-MCI组增高.结论 3种不同亚型MCI认知损害均为多区域性,aMCI主要表现为记忆损害,V-MCI以执行功能损害为主,PD-MCI记忆及执行功能均受损;aMCI较其他亚型更易出现抑郁倾向.不同亚型MCI神经心理学特征的不同,反映了不同的病理生理学机制.     

慢性失眠患者数字工作记忆的功能磁共振研究

目的 探讨慢性失眠患者数字工作记忆神经网络连接的改变.方法 采用组块设计方法,分别对40例慢性失眠患者(失眠组)及50例正常睡眠者(对照组)进行数字工作记忆状态下功能磁共振扫描,比较两组受试者在数字工作记忆中反应时间及正确率以及编码、维持、提取阶段脑区激活强度的改变.结果 失眠组与对照组数字工作记忆正确率的比较差异无统计学意义(P＞0.05),失眠组反应时间明显增加,差异有统计学意义(P＜0.01).慢性失眠患者在数字工作记忆编码期激活强度增强的脑区为左侧壳核、豆状核、顶下小叶及右侧尾状核、右枕叶;维持期激活强度增强的脑区为右侧额叶,左侧额叶及额叶内侧面,而左侧额上回激活强度有所下降;提取期激活强度增强的脑区为右额下回及右顶下缘角回,而激活轻度下降的脑区则有左内侧额上回、左岛叶、左后扣带回、左颞上回、左额上回及右颞叶、右后扣带回.结论 慢性失眠患者在数字工作记忆的各阶段,脑区激活强度较健康人有所改变:大脑皮质和皮质下结构广泛受损,即其神经网络连接发生明显改变.     

Different mechanisms of episodic memory failure in mild cognitive impairment

Mild cognitive impairment (MCI), defined as episodic memory impairment beyond what is expected in normal aging, is often associated with hippocampal atrophy (HA) and may represent incipient Alzheimer's disease. However, recent studies suggest that MCI is very heterogeneous and multiple etiologies likely exist. One possibility is small vessel cerebrovascular disease (CVD). Specifically, we hypothesized that white matter hyperintensities (WMH), an MRI marker for CVD, would lead to impairments in executive control processes critical for working memory that may, in turn, result in episodic memory impairment. To test this hypothesis, we examined a group of subjects clinically diagnosed with MCI and used MRI to further subcategorize individuals as either MCI with severe white matter hyperintensities (MCI-WMH) or MCI with severe hippocampal atrophy (MCI-HA). MCI-WMH, MCI-HA, and matched control subjects each performed a battery of working memory and episodic memory tasks. Results showed that MCI-HA and MCI-WMH were equally impaired on the episodic memory task relative to controls, but MCI-WMH were additionally impaired on tests tapping verbal and spatial working memory abilities and attentional control processes. These results suggest that CVD and hippocampal dysfunction are associated with distinct neuropsychological profiles. Although both syndromes are associated with episodic memory deficits, CVD is additionally associated with working memory and executive control deficits.     

Episodic memory and regional atrophy in frontotemporal lobar degeneration

It has been unclear to what extent memory is affected in frontotemporal lobar degeneration (FTLD). Since patients usually have atrophy in regions implicated in memory function, the frontal and/or temporal lobes, one would expect some memory impairment, and that the degree of atrophy in these regions would be inversely related to memory function. The purposes of this study were (1) to assess episodic memory function in FTLD, and more specifically patients' ability to episodically re-experience an event, and determine its source; (2) to examine whether memory performance is related to quantified regional brain atrophy. FTLD patients (n=18) and healthy comparison subjects (n=14) were assessed with cued recall, recognition, "remember/know" (self-reported re-experiencing) and source recall, at 30 min and 24h after encoding. Regional gray matter volumes were assessed with high resolution structural MRI concurrently to testing. Patients performed worse than comparison subjects on all memory measures. Gray matter volume in the left medial temporal lobe was positively correlated with recognition, re-experiencing, and source recall. Gray matter volume in the left posterior temporal lobe correlated significantly with recognition, at 30 min and 24h, and with source recall at 30 min. Estimated familiarity at 30 min was positively correlated with gray matter volume in the left inferior parietal lobe. In summary, episodic memory deficits in FTLD may be more common than previously thought, particularly in patients with left medial and posterior temporal atrophy.     

Episodic memory impairment in patients with Alzheimer’s disease is correlated with entorhinal cortex atrophy

The aims of this study were to investigate the pattern of cortical atrophy and the relationships between memory performances and the brain regions in Alzheimer's Disease (AD). optimized voxel-based morphometry (VBM) was applied to the MRI brain images of 18 probable AD and 18 healthy subjects (HS). Patients performed verbal and visuo-spatial episodic and shortterm memory tests. Contrasting of AD group with HS, and anatomobehavioural correlations were carried out in order to identify regional atrophic changes and neuro-cognitive aspects in AD group. We found evidence of gray matter (GM) volume reduction in AD in the medial temporal, parietal and frontal areas bilaterally and in the left anterior thalamic nuclei. Performance on the episodic memory delayed recall tests co-varied with GM volume in the left entorhinal cortex. The pattern of cortical atrophy likely reflects the heterogeneous level of dementia severity in our AD group. The anatomical region affected in the left hemisphere indicates a sufferance at multiple levels of the Polysynaptic Hippocampal Pathway, which is involved in declarative memory. Findings on the entorhinal cortex and the delayed memory scores support the role of the entorhinal cortex in episodic memory. Damage to the entorhinal cortex, deafferenting the hippocampus from neocortical inputs, interferes with episodic memory consolidation in AD patients.     

Relation between medial temporal atrophy and functional brain activity during memory processing in Alzheimer's disease: a combined MRI and SPECT study

OBJECTIVE: To investigate the relation between atrophy of the hippocampal region and brain functional patterns during episodic memory processing in Alzheimer's disease. PATIENTS AND METHODS: Whole brain structural magnetic resonance imaging (MRI) data and single photon emission computed tomography (SPECT) measures of regional cerebral blood flow (rCBF) were obtained during a verbal recognition memory task in nine subjects with mild Alzheimer's disease and 10 elderly healthy controls. Using the statistical parametric mapping approach, voxel based comparisons were made on the MRI data to identify clusters of significantly reduced grey matter concentrations in the hippocampal region in the Alzheimer patients relative to the controls. The mean grey matter density in the voxel cluster of greatest hippocampal atrophy was extracted for each Alzheimer subject. This measure was used to investigate, on a voxel by voxel basis, the presence of significant correlations between the degree of hippocampal atrophy and the rCBF SPECT measures obtained during the memory task. RESULTS: Direct correlations were detected between the hippocampal grey matter density and rCBF values in voxel clusters located bilaterally in the temporal neocortex, in the left medial temporal region, and in the left posterior cingulate cortex during the memory task in the Alzheimer's disease group (p < 0.001). Conversely, measures of hippocampal atrophy were negatively correlated with rCBF values in voxel clusters located in the frontal lobes, involving the right and left inferior frontal gyri and the insula (p < 0.001). CONCLUSIONS: Hippocampal atrophic changes in Alzheimer's disease are associated with reduced functional activity in limbic and associative temporal regions during episodic memory processing, but with increased activity in frontal areas, possibly on a compensatory basis.     

Structural and metabolic correlates of episodic memory in relation to the depth of encoding in normal aging

This study set out to establish the relationship between changes in episodic memory retrieval in normal aging on the one hand and gray matter volume and (18)FDG uptake on the other. Structural MRI, resting-state (18)FDG-PET, and an episodic memory task manipulating the depth of encoding and the retention interval were administered to 46 healthy subjects divided into three groups according to their age (young, middle-aged, and elderly adults). Memory decline was found not to be linear in the course of normal aging: Whatever the retention interval, the retrieval of shallowly encoded words was impaired in both the middle-aged and the elderly, whereas the retrieval of deeply encoded words only declined in the elderly. In middle-aged and elderly subjects, the reduced performance in the shallow encoding condition was mainly related to posterior mediotemporal volume and metabolism. By contrast, the impaired retrieval of deeply encoded words in the elderly group was mainly related to frontal and parietal regions, suggesting the adoption of inefficient strategic processes.     

Multiple diffusion indices reveals white matter degeneration in Alzheimer's disease and mild cognitive impairment: a tract-based spatial statistics study

Alzheimer's disease (AD) is a progressive neurodegenerative disease involving the decline of memory and other cognitive functions. Mild cognitive impairment (MCI) represents a transition phase between normal aging and early AD. The degeneration patterns of the white matter across the brain in AD and MCI remain largely unclear. Here we used diffusion tensor imaging and tract-based spatial statistics (TBSS) to investigate white matter changes in multiple diffusion indices (e.g., fractional anisotropy, axial, radial and mean diffusivities) in both AD and MCI patients. Compared with the normal controls, the AD patients had reduced fractional anisotropy and increased axial, radial and mean diffusivities in widespread white matter structures, including the corpus callosum and the white matter of lateral temporal cortex, the posterior cingulate cortex/precuneus and the fronto-parietal regions. Similar white matter regions with reduced anisotropy were also found in MCI patients but with a much less extent than in AD. Between the AD and MCI groups, there were significant differences in the axial and mean diffusivities of the white matter tracts adjacent to the posterior cingulate cortex/precuneus without anisotropy changes. Taken together, our findings based upon multiple diffusion indices (FA, axial, radial and mean diffusivities) suggest distinct degeneration behaviors of the white matter in AD and MCI.     

Spatial patterns of intrinsic brain activity in mild cognitive impairment and Alzheimer's disease: a resting-state functional MRI study

We used resting-state functional MRI to investigate spatial patterns of spontaneous brain activity in 22 healthy elderly subjects, as well as 16 mild cognitive impairment (MCI) and 16 Alzheimer's disease (AD) patients. The pattern of intrinsic brain activity was measured by examining the amplitude of low-frequency fluctuations (ALFF) of blood oxygen level dependent signal during rest. There were widespread ALFF differences among the three groups throughout the frontal, temporal, and parietal cortices. Both AD and MCI patients showed decreased activity mainly in the medial parietal lobe region and lentiform nucleus, while there was increased activity in the lateral temporal regions and superior frontal and parietal regions as compared with controls. Compared with MCI, the AD patients showed decreased activity in the medial prefrontal cortex and increased activity in the superior frontal gyrus and inferior and superior temporal gyri. Specifically, the most significant ALFF differences among the groups appeared in the posterior cingulate cortex, with a reduced pattern of activity when comparing healthy controls, MCI, and AD patients. Additionally, we also showed that the regions with ALFF changes had significant correlations with the cognitive performance of patients as measured by mini-mental state examination scores. Finally, while taking gray matter volume as covariates, the ALFF results were approximately consistent with those without gray matter correction, implying that the functional analysis could not be explained by regional atrophy. Together, our results demonstrate that there is a specific pattern of ALFF in AD and MCI, thus providing insights into biological mechanisms of the diseases.     

Brain regions associated with episodic retrieval in normal aging and Alzheimer's disease.

OBJECTIVE: To examine patterns of brain activation during verbal episodic retrieval in normal elderly subjects and patients in an early phase of AD. BACKGROUND: It is established that 1) a profound episodic memory impairment is a cardinal symptom of AD; and 2) some of the earliest brain changes in this disease occur in regions critical to episodic memory, such as the hippocampus and neighboring regions. Yet, it remains largely unknown whether the episodic memory deficit seen in AD is paralleled by concomitant alterations in brain activity during actual task performance in these or other brain areas. METHODS: Using PET, blood flow was assessed in normal elderly subjects and patients with early AD during two retrieval conditions involving completion of word stems: baseline and cued recall. RESULTS: The patients with AD showed a marked performance deficit in cued recall, although the two groups were indistinguishable in the baseline task condition. Both groups showed bilateral activity in orbital and dorsolateral prefrontal cortex, left precuneus, and right cerebellum, as well as decreased activity in distinct left temporal regions during cued recall. The normal elderly alone activated the left parietal cortex and the left hippocampal formation during episodic retrieval. By contrast, AD-related increases in activity during cued recall were observed in the left orbital prefrontal cortex and left cerebellum. CONCLUSIONS: The similar patterns of activations in the two groups suggest that a large distributed network involved in episodic memory retrieval functions relatively normally in early AD. Those retrieval activations seen in the normal elderly, as opposed to the patients, may reflect AD-related failures in semantic processing and successful recollection of the target information, respectively. Finally, the AD-related increases in activity were interpreted in terms of compensatory reactions to the difficulties in performing the episodic memory task.     

Brain function during multi-trial learning in mild cognitive impairment: a PET activation study

We explored functional brain changes with positron emission tomography (PET) in mild cognitive impairment (MCI) patients and elderly normal controls by employing an episodic memory task that included two successive encoding trials of semantically related word-pairs and final retrieval. Both groups demonstrated significant learning across the two trials. The control group showed predominantly left frontal activity during encoding, and right frontal plus left temporal activity during retrieval. However, the MCI patients recruited partly different brain regions. They failed to activate right frontal and left temporal areas during retrieval, and failed to show any different activation for encoding on the first and second trials, whereas the controls activated a region of posterior cingulate. There was indication of compensatory increases in rCBF of the occipital cortex during incremental learning and the left frontal lobe during retrieval in the patients. These results suggest different episodic memory processing in the MCI group, and a possible over-reliance on semantic processing. Subtle functional changes occur in the pre-Alzheimer brain before there are marked structural or behavioural abnormalities.     

Normal aging modulates prefrontoparietal networks underlying multiple memory processes

A functional decline of brain regions underlying memory processing represents a hallmark of cognitive aging. Although a rich literature documents age‐related differences in several memory domains, the effect of aging on networks that underlie multiple memory processes has been relatively unexplored. Here we used functional magnetic resonance imaging during working memory and incidental episodic encoding memory to investigate patterns of age‐related differences in activity and functional covariance patterns common across multiple memory domains. Relative to younger subjects, older subjects showed increased activation in left dorso‐lateral prefrontal cortex along with decreased deactivation in the posterior cingulate. Older subjects showed greater functional covariance during both memory tasks in a set of regions that included a positive prefronto‐parietal‐occipital network as well as a negative network that spanned the default mode regions. These findings suggest that the memory process‐invariant recruitment of brain regions within prefronto‐parietal‐occipital network increases with aging. Our results are in line with the dedifferentiation hypothesis of neurocognitive aging, thereby suggesting a decreased specialization of the brain networks supporting different memory networks.