Neuroanatomical and neurocognitive changes associated with subjective cognitive decline.

Introduction: Subjective Cognitive Decline (SCD) can progress to mild cognitive impairment (MCI) and Alzheimer's disease (AD) dementia and thus may represent a preclinical stage of the AD continuum. However, evidence about structural changes observed in the brain during SCD remains inconsistent. Materials and methods: This cross-sectional study aimed to evaluate, in subjects recruited from the CompAS project, neurocognitive and neurostructural differences between a group of forty-nine control subjects and forty-nine individuals who met the diagnostic criteria for SCD and exhibited high levels of subjective cognitive complaints (SCCs). Structural magnetic resonance imaging was used to compare neuroanatomical differences in brain volume and cortical thickness between both groups. Results: Relative to the control group, the SCD group displayed structural changes involving frontal, parietal, and medial temporal lobe regions of critical importance in AD etiology and functionally related to several cognitive domains, including executive control, attention, memory, and language. Conclusion: Despite the absence of clinical deficits, SCD may constitute a preclinical entity with a similar (although subtle) pattern of neuroanatomical changes to that observed in individuals with amnestic MCI or AD dementia.

Cognitive reserve, neurocognitive performance, and high-order resting-state networks in cognitively unimpaired aging.

Cognitive Reserve (CR) is considered a protective factor during the aging process. However, although CR is a multifactorial construct, it has been operationalized in a unitary way (years of formal education or IQ). In the present study, a validated measure to categorize CR holistically (Cognitive Reserve Index Questionnaire) was used to evaluate the resting-state functional connectivity in 77 cognitively unimpaired participants aged 50 years and over with high and low CR, and matched brain global atrophy levels. The connectivity of networks linked to attentional (Dorsal Attention Network -DAN-) and executive (Frontal-Parietal Control Network -FPCN-) processes were evaluated by the combination of Independent Component Analysis and seed-based approaches, since these networks have been proposed as candidates to underlie the protective effect of CR in the aging context. Participants with high CR showed an increase of the connectivity in the FPCN and a decrease in the DAN with respect to the low CR group, correlating with neuropsychological scores and supporting that high CR is related to a better neurocognitive preservation during aging.

Brain Atrophy and Clinical Characterization of Adults With Mild Cognitive Impairment and Different Cerebrospinal Fluid Biomarker Profiles According to the AT(N) Research Framework of Alzheimer's Disease.

Introduction: This study aimed to evaluate, in adults with mild cognitive impairment (MCI), the brain atrophy that may distinguish between three AT(N) biomarker-based profiles, and to determine its clinical value. Methods: Structural MRI (sMRI) was employed to evaluate the volume and cortical thickness differences in MCI patients with different AT(N) profiles, namely, A-T-(N)-: normal AD biomarkers; A+T-(N)-: AD pathologic change; and A+T+(N)+: prodromal AD. Sensitivity and specificity of these changes were also estimated. Results: An initial atrophy in medial temporal lobe (MTL) areas was found in the A+T-(N)- and A+T+(N)+ groups, spreading toward the parietal and frontal regions in A+T+(N)+ patients. These structural changes allowed distinguishing AT(N) profiles within the AD continuum; however, the profiles and their pattern of neurodegeneration were unsuccessful to determine the current clinical status. Conclusion: sMRI is useful in the determination of the specific brain structural changes of AT(N) profiles along the AD continuum, allowing differentiation between MCI adults with or without pathological AD biomarkers.

Impaired glucose metabolism reduces the neuroprotective action of adipocytokines in cognitively normal older adults with insulin resistance.

Evidence suggests that aging-related dysfunctions of adipose tissue and metabolic disturbances increase the risk of diabetes and metabolic syndrome (MtbS), eventually leading to cognitive impairment and dementia. However, the neuroprotective role of adipocytokines in this process has not been specifically investigated. The present study aims to identify metabolic alterations that may prevent adipocytokines from exerting their neuroprotective action in normal ageing. We hypothesize that neuroprotection may occur under insulin resistance (IR) conditions as long as there are no other metabolic alterations that indirectly impair the action of adipocytokines, such as hyperglycemia. This hypothesis was tested in 239 cognitively normal older adults (149 females) aged 52 to 87 years (67.4 ± 5.9 yr). We assessed whether the homeostasis model assessment-estimated insulin resistance (HOMA-IR) and the presence of different components of MtbS moderated the association of plasma adipocytokines (i.e., adiponectin, leptin and the adiponectin to leptin [Ad/L] ratio) with cognitive functioning and cortical thickness. The results showed that HOMA-IR, circulating triglyceride and glucose levels moderated the neuroprotective effect of adipocytokines. In particular, elevated triglyceride levels reduced the beneficial effect of Ad/L ratio on cognitive functioning in insulin-sensitive individuals; whereas under high IR conditions, it was elevated glucose levels that weakened the association of the Ad/L ratio with cognitive functioning and with cortical thickness of prefrontal regions. Taken together, these findings suggest that the neuroprotective action of adipocytokines is conditioned not only by whether cognitively normal older adults are insulin-sensitive or not, but also by the circulating levels of triglycerides and glucose, respectively.

Changes in brain activity related to episodic memory retrieval in adults with single domain amnestic mild cognitive impairment.

The present fMRI study aimed to characterize the performance and the brain activity changes related to episodic memory retrieval in adults with single domain aMCI (sdaMCI), relative to cognitively unimpaired adults. Participants performed an old/new recognition memory task with words while BOLD signal was acquired. The sdaMCI group showed lower hits (correct recognition of old words), lower ability to discriminate old and new words, higher errors and longer reaction times for hits. This group also displayed brain hypoactivation in left precuneus and the left midcingulate cortex during the successful recognition of old words. These changes in brain activity suggest the presence of neural dysregulations in brain regions involved during successful episodic memory retrieval. Moreover, hypoactivation in these brain areas discriminated both groups with moderate sensitivity and specificity values, suggesting that it might constitute a potential neurocognitive biomarker of sdaMCI.

Spatiotemporal pattern of brain electrical activity related to immediate and delayed episodic memory retrieval.

In the present study we used the event-related brain potentials (ERP) technique and eLORETA (exact low-resolution electromagnetic tomography) method in order to characterize and compare the performance and the spatiotemporal pattern of the brain electrical activity related to the immediate episodic retrieval of information (words) that is being learned relative to delayed episodic retrieval twenty-minutes later. For this purpose, 16 young participants carried out an old/new word recognition task with source memory (word colour). The task included an immediate memory phase (with three study-test blocks) followed (20 min later) by a delayed memory phase with one test block. The behavioural data showed progressive learning and consolidation of the information (old words) during the immediate memory phase. The ERP data to correctly identified old words for which the colour was subsequently recollected (H/H) compared to the correctly rejected new words (CR) showed: (1) a significant more positive-going potential in the 500-675 ms post-stimulus interval (parietal old/new effect, related to recollection), and (2) a more negative-going potential in the 950-1850 ms interval (LPN effect, related to retrieval and post-retrieval processes). The eLORETA data also revealed that the successful recognition of old words (and probably retrieval of their colour) was accompanied by activation of (1) left medial temporal (parahippocampal gyrus) and parietal regions involved in the recollection in both memory phases, and (2) prefrontal regions and the superior temporal gyrus (in the immediate and delayed memory phases respectively) involved in monitoring, evaluating and maintaining the retrieval products. These findings indicate that episodic memory retrieval depends on a network involving medial temporal lobe and frontal, parietal and temporal neocortical structures. That network was involved in immediate and delayed memory retrieval and during the course of memory consolidation, with greater activation of some nodes (mobilization of more processing resources) for the delayed respect to the immediate retrieval condition.

The importance of age in the search for ERP biomarkers of aMCI.

Alzheimer's Disease (AD) has become a major health issue in recent decades, and there is now growing interest in amnestic mild cognitive impairment (aMCI), an intermediate stage between healthy aging and dementia, usually AD. Event-related brain potential (ERP) studies have sometimes failed to detect differences between aMCI and control participants in the Go-P3 (or P3b, related to target classification processes in a variety of tasks) and NoGo-P3 (related to response inhibition processes, mainly in Go/NoGo tasks) ERP components. The aim of the present study was to evaluate whether the age factor, which is not usually taken into account in ERP studies, modulates group differences in these components. With this aim, we divided two groups of volunteer participants, 34 subjects with aMCI (51-87 years) and 31 controls (52-86 years), into two age subgroups: 69 years or less and 70 years or more. We recorded brain activity while the participants performed a distraction-attention auditory-visual (AV) task. Task performance was poorer in the older than in the younger group, and aMCI participants produced fewer correct responses than the matched controls; but no interactions of the age and group factors on performance were found. On the other hand, Go-P3 and NoGo-N2 latencies were longer in aMCI participants than in controls only in the younger subgroup. Thus, the younger aMCI participants categorized the Go stimuli in working memory and processed the NoGo stimuli (which required response inhibition) slower than the corresponding controls. Finally, the combination of the number of hits, Go-P3 latency and NoGo-N2 latency yielded acceptable sensitivity and specificity scores (0.70 and 0.92, respectively) as regards distinguishing aMCI participants aged 69 years or less from the age-matched controls. The findings indicate age should be taken into account in the search for aMCI biomarkers.

Effects of Mild Cognitive Impairment on the Event-Related Brain Potential Components Elicited in Executive Control Tasks.

We summarize here the findings of several studies in which we analyzed the event-related brain potentials (ERPs) elicited in participants with mild cognitive impairment (MCI) and in healthy controls during performance of executive tasks. The objective of these studies was to investigate the neural functioning associated with executive processes in MCI. With this aim, we recorded the brain electrical activity generated in response to stimuli in three executive control tasks (Stroop, Simon, and Go/NoGo) adapted for use with the ERP technique. We found that the latencies of the ERP components associated with the evaluation and categorization of the stimuli were longer in participants with amnestic MCI than in the paired controls, particularly those with multiple-domain amnestic MCI, and that the allocation of neural resources for attending to the stimuli was weaker in participants with amnestic MCI. The MCI participants also showed deficient functioning of the response selection and preparation processes demanded by each task.

Increased Amplitude of the P3a ERP Component as a Neurocognitive Marker for Differentiating Amnestic Subtypes of Mild Cognitive Impairment.

The event-related potential (ERP) technique has been shown to be useful for evaluating changes in brain electrical activity associated with different cognitive processes, particularly in Alzheimer's disease (AD). Longitudinal studies have shown that a high proportion of people with amnestic mild cognitive impairment (aMCI) go on to develop AD. aMCI is divided into two subtypes according to the presence of memory impairment only (single-domain aMCI: sdaMCI) or impairment of memory and other cognitive domains (multi-domain aMCI: mdaMCI). The main aim of this study was to examine the effects of sdaMCI and mdaMCI on the P3a ERP component associated with the involuntary orientation of attention toward unattended infrequent novel auditory stimuli. Participants performed an auditory-visual distraction-attention task, in which they were asked to ignore the auditory stimuli (standard, deviant, and novel) and to attend to the visual stimuli (responding to some of them: Go stimuli). P3a was identified in the Novel minus Standard difference waveforms, and reaction times (RTs) and hits (in response to Go stimuli) were also analyzed. Participants were classified into three groups: Control, 20 adults (mean age (M): 65.8 years); sdaMCI, 19 adults (M: 67 years); and mdaMCI, 11 adults (M: 71 years). In all groups, the RTs were significantly longer when Go stimuli were preceded by novel (relative to standard) auditory stimuli, suggesting a distraction effect triggered by novel stimuli; mdaMCI participants made significantly fewer hits than control and sdaMCI participants. P3a comprised two consecutive phases in all groups: early-P3a (e-P3a), which may reflect the orienting response toward the irrelevant stimuli, and late-P3a (l-P3a), which may be a correlate of subsequent evaluation of these stimuli. The e-P3a amplitude was significantly larger in mdaMCI than in sdaMCI participants, and the l-P3a amplitude was significantly larger in mdaMCI than in sdaMCI and Control participants, indicating greater involuntary capture of attention to unattended novel auditory stimuli and allocation of more attentional resources for the subsequent evaluation of these stimuli in mdaMCI participants. The e-P3a and l-P3a components showed moderate to high sensitivity and specificity for distinguishing between groups, suggesting that both may represent optimal neurocognitive markers for differentiating aMCI subtypes.

Neurocognitive and Behavioral Indexes for Identifying the Amnestic Subtypes of Mild Cognitive Impairment.

Early identification of amnestic mild cognitive impairment (aMCI) subtypes is important for early diagnosis and prognosis of Alzheimer's disease. Healthy, single-domain (sdaMCI) and multiple-domain aMCI (mdaMCI) participants performed an auditory-visual distraction-attention task. Event-related brain potentials (ERPs) were recorded while the participants performed the task to evaluate Go/NoGo N2 and P3 ERP components. The results showed the expected behavioral and cognitive decline in mdaMCI participants relative to controls (fewer hits, longer reaction times [RTs], slightly smaller Go-N2 and NoGo-N2 amplitudes), while sdaMCI participants showed some decline (slightly longer RTs, smaller Go- and NoGo-N2 amplitudes) along with some unexpected results (a late positive slow wave, PSW) and good levels of execution. In addition, some of these parameters proved to be useful markers. Thus, the number of hits was the best marker for diagnosing mdaMCI participants (distinguishing them from controls, from sdaMCI participants, and from both groups together), while the PSW amplitude was the best marker for diagnosing sdaMCI participants (distinguishing them from controls, and from control & mdaMCI participants).

Involuntary Capture and Voluntary Reorienting of Attention Decline in Middle-Aged and Old Participants.

The main aim of this study was to examine the effects of aging on event-related brain potentials (ERPs) associated with the automatic detection of unattended infrequent deviant and novel auditory stimuli (Mismatch Negativity, MMN) and with the orienting to these stimuli (P3a component), as well as the effects on ERPs associated with reorienting to relevant visual stimuli (Reorienting Negativity, RON). Participants were divided into three age groups: (1) Young: 21-29 years old; (2) Middle-aged: 51-64 years old; and (3) Old: 65-84 years old. They performed an auditory-visual distraction-attention task in which they were asked to attend to visual stimuli (Go, NoGo) and to ignore auditory stimuli (S: standard, D: deviant, N: novel). Reaction times (RTs) to Go visual stimuli were longer in old and middle-aged than in young participants. In addition, in all three age groups, longer RTs were found when Go visual stimuli were preceded by novel relative to deviant and standard auditory stimuli, indicating a distraction effect provoked by novel stimuli. ERP components were identified in the Novel minus Standard (N-S) and Deviant minus Standard (D-S) difference waveforms. In the N-S condition, MMN latency was significantly longer in middle-aged and old participants than in young participants, indicating a slowing of automatic detection of changes. The following results were observed in both difference waveforms: (1) the P3a component comprised two consecutive phases in all three age groups-an early-P3a (e-P3a) that may reflect the orienting response toward the irrelevant stimulation and a late-P3a (l-P3a) that may be a correlate of subsequent evaluation of the infrequent unexpected novel or deviant stimuli; (2) the e-P3a, l-P3a, and RON latencies were significantly longer in the Middle-aged and Old groups than in the Young group, indicating delay in the orienting response to and the subsequent evaluation of unattended auditory stimuli, and in the reorienting of attention to relevant (Go) visual stimuli, respectively; and (3) a significantly smaller e-P3a amplitude in Middle-aged and Old groups, indicating a deficit in the orienting response to irrelevant novel and deviant auditory stimuli.

Information processing becomes slower and predominantly serial in aging: Characterization of response-related brain potentials in an auditory-visual distraction-attention task.

The aim of this study was to evaluate the effects of aging and attentional capture provoked by novel auditory stimuli on behavior (reaction time [RT], hits) and on response-related brain potentials (preRFP, CRN, postRFP, parietalRP) to target visual stimuli. Twenty-two young, 27 middle-aged, and 24 old adults performed an auditory-visual distraction-attention task. The RTs and latencies of preRFP, postRFP and parietalRT were longer in old and middle-aged than in young participants, reflecting the well-established age-related slowing of processing and performance. The inter-peak latencies (P3b-preRFP, preRFP-parietalRP, parietalRP-postRFP) were also longer in old and middle-aged than in young participants, further indicating an age-related tendency to increased predominance of serial (rather than parallel) processing of information, and that preRFP, CRN, postRFP, and parietalRP represent different cognitive processes from those indexed by the stimulus-related P3b. Finally, a distraction effect in performance (all three groups) and in postRFP latency (only middle-aged group) was also observed.

Effects of aging and involuntary capture of attention on event-related potentials associated with the processing of and the response to a target stimulus.

The main aim of the present study was to assess whether aging modulates the effects of involuntary capture of attention by novel stimuli on performance, and on event-related potentials (ERPs) associated with target processing (N2b and P3b) and subsequent response processes (stimulus-locked Lateralized Readiness Potential -sLRP- and response-locked Lateralized Readiness Potential -rLRP-). An auditory-visual distraction-attention task was performed by 77 healthy participants, divided into three age groups (Young: 21-29, Middle-aged: 51-64, Old: 65-84 years old). Participants were asked to attend to visual stimuli and to ignore auditory stimuli. Aging was associated with slowed reaction times, target stimulus processing in working memory (WM, longer N2b and P3b latencies) and selection and preparation of the motor response (longer sLRP and earlier rLRP onset latencies). In the novel relative to the standard condition we observed, in the three age groups: (1) a distraction effect, reflected in a slowing of reaction times, of stimuli categorization in WM (longer P3b latency), and of motor response selection (longer sLRP onset latency); (2) a facilitation effect on response preparation (later rLRP onset latency), and (3) an increase in arousal (larger amplitudes of all ERPs evaluated, except for N2b amplitude in the Old group). A distraction effect on the stimulus evaluation processes (longer N2b latency) were also observed, but only in middle-aged and old participants, indicating that the attentional capture slows the stimulus evaluation in WM from early ages (from 50 years onwards, without differences between middle-age and older adults), but not in young adults.

Age-related effects on event-related brain potentials in a congruence/incongruence judgment color-word Stroop task.

We examined the event-related brain potentials elicited by color-word stimuli in a Stroop task in which healthy participants (young and old) had to judge whether the meaning and the color of the stimulus were congruent or incongruent. The Stroop effect occurred in both age groups, with longer reaction times in the older group than in the young group for both types of stimuli, but no difference in the number of errors made by either group. Although the N2 and P3b latencies were longer in the older than in the younger group, there were no differences between groups in the latencies of earlier event-related potential components, and therefore the age-related processing slowing is not generalized. The frontal P150 amplitude was larger, and the parietal P3b amplitude was smaller, in the older than in the younger group. Furthermore, the P3b amplitude was maximal at frontal locations in older participants and at parietal locations in young participants. The age-related increase in perceptual resources and the posterior-to-anterior shift in older adults support adaptive reorganization of the neural networks involved in the processing of this Stroop-type task.

Effects of amnestic mild cognitive impairment on N2 and P3 Go/NoGo ERP components.

Although many studies have demonstrated decline in attention and executive function (especially in inhibitory control) in healthy aging and Alzheimer's disease (AD), similar studies concerning mild cognitive impairment (MCI) are scarce. In the present study, we evaluated how the cognitive decline associated with amnestic MCI (aMCI) affects these processes, analyzing the N2 and P3 components of event-related potentials (ERPs) during the response (Go) and inhibition of response (NoGo) to different stimuli. ERPs were analyzed in 63 healthy and 30 aMCI adults (aged 50 to 87 years) during performance of a Go/NoGo auditory-visual attention-distraction task. aMCI adults showed poorer execution (longer response times and fewer correct responses) and smaller Go-N2 and NoGo-N2 amplitudes than control adults, whereas P3 amplitudes and N2 and P3 latencies did not differ between the groups. These results show that aMCI is associated with decline in executive function and stimuli evaluation in working memory.

Mismatch negativity (MMN) amplitude as a biomarker of sensory memory deficit in amnestic mild cognitive impairment.

It has been suggested that changes in some event-related potential (ERP) parameters associated with controlled processing of stimuli could be used as biomarkers of amnestic mild cognitive impairment (aMCI). However, data regarding the suitability of ERP components associated with automatic and involuntary processing of stimuli for this purpose are not conclusive. In the present study, we studied the Mismatch Negativity (MMN) component, a correlate of the automatic detection of changes in the acoustic environment, in healthy adults and adults with aMCI (age range: 50-87 years). An auditory-visual attention-distraction task, in two evaluations separated by an interval of between 18 and 24 months, was used. In both evaluations, the MMN amplitude was significantly smaller in the aMCI adults than in the control adults. In the first evaluation, such differences were observed for the subgroup of adults between 50 and 64 years of age, but not for the subgroup of 65 years and over. In the aMCI adults, the MMN amplitude was significantly smaller in the second evaluation than in the first evaluation, but no significant changes were observed in the control adult group. The MMN amplitude was found to be a sensitive and specific biomarker of aMCI, in both the first and second evaluation.

An event-related potentials study of face naming: evidence of phonological retrieval deficit in the tip-of-the-tongue state.

A famous-face naming task was used to establish the electrophysiological characterization of the tip-of-the-tongue (TOT) state, successful naming (K), and nonrecognition (DK). The differences in the direct event-related potentials (ERPs) and in the lateralized readiness potential between those categories were studied. The ERP correlates of recognition and access to semantic and lexical information were similar between K and TOT, but showed amplitude differences with respect to DK. A delayed onset of the response selection was obtained in TOT in comparison with K, suggesting an insufficient activation of phonological information from 360 ms onwards. The continuous search for the name and the conflict monitoring in TOT led to differences in ERP amplitudes between TOT and the other categories from 750 ms onwards as well as to a delayed onset of response preparation, indicating a continuous engagement of processing resources.

Brain dinamics associated with face-naming and the tip-of-the-tongue state

Las áreas cerebrales más activas y su secuencia de activación durante el recuerdo y la denominación exitosa de caras (Condición SI) y durante el fenómeno de la punta de la lengua (Condición PDL) fueron estimadas a partir de potenciales evocados mediante tomografías electromagnéticas de baja resolución (LORETA). Los resultados muestran evidencia de que una adecuada activación de una red neural (estando principalmente implicadas áreas temporales posteriores, insula, áreas prefrontales mediales y laterales, y áreas temporales mediales) durante los primeros 500 ms después de la presentación de la cara está relacionada con la recuperación exitosa de información léxicofonológica sobre el nombre de la persona. Además se obtuvieron diferencias significativas entre ambas condiciones en el intervalo 538-698 ms; concretamente, el giro cingulado anterior y el área motora suplementaria mostraron una mayor activación en la Condición SI que en la Condición PDL, posiblemente relacionada con la respuesta motora y como consecuencia de la recuperación exitosa de la información léxico-fonológica sobre la persona (AU)

Active brain areas and their temporal sequence of activation during the successful retrieval and naming of famous faces (KNOW) and during the tip-of-the-tongue (TOT) state were studied by means of low resolution electromagnetic tomographic analysis (LORETA) applied to event-related potentials. The results provide evidence that adequate activation of a neural network during the first 500 ms following presentation of the photograph -mainly involving the posterior temporal region, the insula, lateral and medial prefrontal areas and the medial temporal lobe- is associated with successful retrieval of lexical-phonological information about the person’s name. Significant differences between conditions were observed in the 538-698-ms interval; specifically there was greater activation of the anterior cingulate gyrus (ACC) towards the supplementary motor area (SMA) in the KNOW than in the TOT condition, possibly in relation to the motor response and as a consequence of the successful retrieval of lexical-phonological information about the person (AU)

Brain dynamics associated with face-naming and the tip-of-the-tongue state.

Active brain areas and their temporal sequence of activation during the successful retrieval and naming of famous faces (KNOW) and during the tip-of-the-tongue (TOT) state were studied by means of low resolution electromagnetic tomographic analysis (LORETA) applied to event-related potentials. The results provide evidence that adequate activation of a neural network during the first 500 ms following presentation of the photograph--mainly involving the posterior temporal region, the insula, lateral and medial prefrontal areas and the medial temporal lobe--is associated with successful retrieval of lexical-phonological information about the person's name. Significant differences between conditions were observed in the 538-698-ms interval; specifically there was greater activation of the anterior cingulate gyrus (ACC) towards the supplementary motor area (SMA) in the KNOW than in the TOT condition, possibly in relation to the motor response and as a consequence of the successful retrieval of lexical-phonological information about the person.

The effect of aging on movement related cortical potentials during a face naming task.

In the present study a face naming reaction time task was employed in order to evaluate the effect of age on performance and on movement related cortical potentials (MRCPs). In addition, the effect of three response categories with different cognitive demands (DON'T KNOW-don't know the name-, KNOW-correct naming- and TOT-tip-of the-tongue state) on performance and on MRCPs in a sample of older adults was evaluated. The same MRCPs found in a previous study in a sample of young adults were identified in older adults. The results indicated that older participants were generally slower at providing responses than young adults, and that both age groups showed longer reaction time in TOT than in DON'T KNOW and KNOW categories. The first component of readiness potential (1st-RP) showed larger amplitude and longer duration in older than in young adults, especially in the TOT category, which would explain the generally slower responses provided by older participants. In addition, in older adults, the 1st-RP was larger in TOT than in the DON'T KNOW category, but a slope reduction and stabilization were observed in TOT from the more demanding stages of stimulus processing. These results may reflect a lengthening in the preparation period in the TOT category, which probably explains the behavioural slowing in this category. The data of the present study suggest differences in the allocation of processing resources between groups, indicating that the sensoriomotor performance should be compromised more in older than in young adults in tasks with high cognitive load.