Normal McCollough effect in Alzheimer’s disease and global amnesia

The McCollough effect (ME), a long-lasting, pattern-contingent aftereffect in normal human vision, was examined in persons with known deficits in memory. We induced MEs in 11 subjects, 5 patients with various severities of Alzheimer’s disease (AD), H.M. (a patient who has global amnesia due to bilateral medial temporal lobectomy and who has been studied for 35 years since his operation), and 5 control subjects. H.M. and the AD patients showed MEs of strength and duration comparable to those of the control subjects. These results demonstrate a dissociation between learning mechanisms that mediate recall and recognition versus mechanisms that mediate the ME. Furthermore, knowledge about the sites of neuropathology in H.M. and in AD are consistent with other sources of evidence implicating early visual areas, especially V1, as a critical locus of the ME.     

McCollough effect: A neural network model based on source separation

McCollough effects (MEs) are a group of visual contingent aftereffects that involve colour and contour. These effects have been the subject of a large body of literature concerning their properties and theoretical accounts, but the mechanisms underlying the ME have never been fully clarified. We make the assumption that a general adaptive neural process tending to maintain independent dimensions in visual perception could account for the ME. The proposed neural network model generating the ME, though of minimal complexity, can reproduce various detailed experimental results (such as the tilt effect contingent to colour) and above all it accounts for the distinctive long temporal persistence of this aftereffect.     

Familiarity,Target Set and False Positives in Face Recognition

Distinctiveness of a face predicts both miss errors (MEs) and false positives (FPs) but correlations between these errors are low (e.g. Hancock, Burton, & Bruce, 1996). To investigate this, distinctiveness and personal familiarity were analysed as predictors of MEs and FPs in a face recognition experiment. Faces were assigned to three groups, which meant that each set were distractor faces for two different sets of targets. Mean ratings of distinctiveness predicted MEs, whereas familiarity predicted FPs only if individual ratings were used. The degree to which subjects were consistent in their ratings and performance over different faces was also considered. Good subject consistency was found on FPs when the subjects saw the same target faces. If subjects who had seen different target faces were compared, then the consistency of FPs was lower than the consistency of MEs. The results imply that distinctiveness predicts MEs as a general property of the population of faces, whereas familiarity predicts FPs according to the idiosyncrasies of subjects.     

Practice effects on motor control in healthy seniors and patients with mild cognitive impairment and Alzheimer's disease

This research was designed to test the hypothesis that motor practice can enhance the capabilities of motor control in healthy controls (NC) and patients with a diagnosis of probable Alzheimer's disease (AD) and mild cognitive impairment (MCI), and consequently results in better motor performance. Approximately half of the subjects in the NC (n = 31), AD (n = 28), and MCI (n = 29) either received or did not receive practice on a task of fast and accurate arm movement with a digitizer. Changes in movement time (MT), movement smoothness (jerk), and percentage of primary submovement (PPS) were recorded and compared among the three groups across six blocks of trials (baseline and five training sessions). For all subjects, practice improved motor functions as reflected by faster and smoother motor execution, as well as a greater proportion of programming control. Compared to unaffected matched controls, AD and MCI subjects exhibited a greater reduction in movement jerk due to practice. Movement time and PPS data revealed that motor practice appeared to reduce the use of "on-line" correction adopted by the AD or MCI patients while performing the aiming movements. Evidently, their arm movements were quicker, smoother, and temporally more consistent than their untrained peers. The findings of this study shed light on how MCI and AD may affect motor control mechanisms, and suggest possible therapeutic interventions aimed at improving motor functioning in these impaired individuals.     

Practice Effects on Motor Control in Healthy Seniors and Patients with Mild Cognitive Impairment and Alzheimer's Disease

ABSTRACT

This research was designed to test the hypothesis that motor practice can enhance the capabilities of motor control in healthy controls (NC) and patients with a diagnosis of probable Alzheimer's disease (AD) and mild cognitive impairment (MCI), and consequently results in better motor performance. Approximately half of the subjects in the NC (n = 31), AD (n = 28), and MCI (n = 29) either received or did not receive practice on a task of fast and accurate arm movement with a digitizer. Changes in movement time (MT), movement smoothness (jerk), and percentage of primary submovement (PPS) were recorded and compared among the three groups across six blocks of trials (baseline and five training sessions). For all subjects, practice improved motor functions as reflected by faster and smoother motor execution, as well as a greater proportion of programming control. Compared to unaffected matched controls, AD and MCI subjects exhibited a greater reduction in movement jerk due to practice. Movement time and PPS data revealed that motor practice appeared to reduce the use of “on-line” correction adopted by the AD or MCI patients while performing the aiming movements. Evidently, their arm movements were quicker, smoother, and temporally more consistent than their untrained peers. The findings of this study shed light on how MCI and AD may affect motor control mechanisms, and suggest possible therapeutic interventions aimed at improving motor functioning in these impaired individuals.     

Further evidence against the classical conditioning model of McCollough effects

McCollough effects (MEs) have been portrayed by Murch (1976) as classically conditioned responses which result from the pairing of color (unconditioned stimulus) with line orientation (conditioned stimulus). In the present experiment, we sought evidence that ME characteristics resembled those of undisputed conditioned responses. According to Rescorla (1968) and others, conditioned responses may not develop if the unconditioned stimulus is presented in the absence as well as in the presence of the conditioned stimulus. However, in our experiment, MEs induced by inspection sequences containing presentations of color alone in addition to color/ contour pairs were not weaker than controls. This discrepancy challenges the applicability of the conditioning model to MEs.     

Practice does not facilitate acquisition of McCollough effects: Evidence against a learning model

Previous investigators (Schmidt, Pinetts, & Finke, 1978) have asserted that McCollough effects (MEs) are acquired more readily by experienced than by inexperienced subjects. The present experiments examine this claim in a paradigm that utilizes quantitative measurements of MEs to evaluate possible changes in subjects’ susceptibility to them. MEs were induced every few days for approximately 2 months; results revealed no progressive increments in either strength or acquisition rats. The lack of facilitation due to practice is inconsistent with learning models proposed to account for MEs.     

Brain lateralization of phonological awareness varies by maternal education

Socioeconomic status (SES) has been shown to influence language skills, with children of lower SES backgrounds performing worse on language assessments compared to their higher SES peers. While there is abundant behavioral research on the effects of SES, whether there are differences in the neural mechanisms used to support language skill is less established. In this study, we examined the relation between maternal education (ME), a component of SES, and neural mechanisms of language. We focused on Kindergarten children, at the beginning of formal reading education, and on a pre‐reading skill, phonological awareness—the ability to distinguish or manipulate the sounds of language. We determined ME‐related differences in neural activity by examining a skill‐matched sample of typically achieving 5‐year‐old children as they performed a rhyme judgment task. We examined brain lateralization in two language processing regions, the inferior frontal gyrus (IFG) and superior temporal gyrus (STG). In the IFG, lateralization was related to ME but not skill: children with low ME showed bilateral activation compared to children with higher ME who showed leftward lateralization. In the STG, there was a skill by ME interaction on lateralization, such that children with high ME showed a positive relation between rightward lateralization and skill and children with low ME showed a positive relation between leftward lateralization and skill. Thus, we demonstrated ME is related to differences in neural recruitment during language processing, yet this difference in recruitment is not indicative of a deficit in linguistic processing in Kindergarten children.     

One size does not fit all: face emotion processing impairments in semantic dementia, behavioural-variant frontotemporal dementia and Alzheimer's disease are mediated by distinct cognitive deficits

Patients with frontotemporal dementia (both behavioural variant [bvFTD] and semantic dementia [SD]) as well as those with Alzheimer's disease (AD) show deficits on tests of face emotion processing, yet the mechanisms underlying these deficits have rarely been explored. We compared groups of patients with bvFTD (n = 17), SD (n = 12) or AD (n = 20) to an age- and education-matched group of healthy control subjects (n = 36) on three face emotion processing tasks (Ekman 60, Emotion Matching and Emotion Selection) and found that all three patient groups were similarly impaired. Analyses of covariance employed to partial out the influences of language and perceptual impairments, which frequently co-occur in these patients, provided evidence of different underlying cognitive mechanisms. These analyses revealed that language impairments explained the original poor scores obtained by the SD patients on the Ekman 60 and Emotion Selection tasks, which involve verbal labels. Perceptual deficits contributed to Emotion Matching performance in the bvFTD and AD patients. Importantly, all groups remained impaired on one task or more following these analyses, denoting a primary emotion processing disturbance in these dementia syndromes. These findings highlight the multifactorial nature of emotion processing deficits in patients with dementia.     

Inductive Reasoning in Alzheimer''s Disease

We evaluated knowledge of basic level and superordinate semantic relations and the role of cognitive resources during inductive reasoning in probable Alzheimer's disease (AD). Nineteen mildly demented AD patients and 17 healthy control subjects judged the truthfulness of arguments with a premise and a conclusion that contain familiar concepts coupled with "blank" predicates, such as "Spiders contain phosphatidylcholine; therefore all insects contain phosphatidylcholine." Like healthy control subjects, AD patients were relatively insensitive to the typicality of the premise category when judging the strength of arguments with a conclusion containing a basic-level concept, but were relatively sensitive to typicality during judgments of arguments containing a superordinate in the conclusion. Moreover, AD patients resembled control subjects in judging arguments with an immediate superordinate in the conclusion compared to arguments with a distant superordinate. AD patients differed from control subjects because they could not take advantage of two premises in an argument containing basic-level concepts. We conclude that semantic knowledge is sufficiently preserved in AD to support inductive reasoning, but that limited cognitive resources may interfere with AD patients' ability to consider the entire spectrum of information available during semantic challenges.     

Pattern of language impairment is different in Alzheimer's disease and multi-infarct dementia.

Language impairment was assessed in 33 patients with Alzheimer's disease (AD), in 52 patients with multi-infarct dementia (MID), and in 86 elderly community residents. The investigation included the D-Test Battery based on the Luria's Neuropsychological Investigation for all subjects. An extended battery of Luria's language items was used for 30 demented patients (11 AD and 19 MID patients) and 86 controls. The changes in language functions in normal subjects could be clearly differentiated from those seen in patients with mild dementia. The patients with different degrees of dementia differed also significantly from each other in regard to language impairment. Moreover, patients with AD and MID appeared to have different patterns of language impairment although the severity of dementia and the levels of orientation, mnestic, and conceptual functions were equal. AD was associated especially with a defect in understanding of grammatical structures and MID with disorders in recognition of words, naming, and repetition. The differential diagnostic capacity of 23 selected language items proved to be 97% between AD, MID, and control subjects. The results indicate that the examination of language functions is valuable in the differential diagnosis of dementia.     

Impairment in the control of coupled cyclic movements of ipsilateral hand and foot after total callosotomy

Integrity of both cerebral hemispheres is required to control in-phase or anti-phase coupling of ipsilateral hand and foot oscillations, as shown by the impairment of these tasks when performed on the healthy side of hemiplegic patients. On this basis, coupling of hand–foot movements was analysed in a right-handed subject (ME) who underwent a total resection of the corpus callosum. Oscillations of the prone hand and foot, paced by a metronome at different frequencies, as well as EMG activity in extensor carpi radialis (ECR) and tibialis anterior (TA) muscles were analysed by measuring the average phase difference between the hand and foot movements and EMG cycles.

ME performed in-phase movements (right-hand extension coupled to right-foot dorsal flexion) at frequencies up to 3 Hz, though the hand cycle progressively lagged the foot cycle as the frequency increased. At 3 Hz the hand lag reached −142° (as compared to about 25° in healthy subjects). The lag increased even further after application of an inertial load to the hand, reaching 180° at 1.8 Hz (about 50° in healthy subjects). ME's hand lag is caused by the lack of any anticipatory reaction in hand movers. In contrast to healthy subjects, which activate the ECR earlier than the TA when the frequency increases, ME activated the ECR later than TA at all frequencies higher than 0.9 Hz.

Anti-phase movements (hand extension coupled to foot plantar flexion) were performed only upto 1 Hz in unloaded conditions. At 0.6 Hz, movements were in tight phase-opposition (3°), but at 1 Hz, the hand lag reached −34° because of a delayed ECR activation. After hand loading ME was unable to couple movements in anti-phase. In contrast, normal subjects maintain a tight anti-phase coupling up to 2.0 Hz, both with an unloaded or loaded hand. Similar deficits were observed by ME when performing in-phase and anti-phase coupling on the left side, as well as when he was blindfolded.

In normal subjects, an anticipated muscular activation of hand movers compensates for hand loading. Since this compensation must depend on monitoring the hand delay induced by loading, the absence in ME of such compensatory reaction suggests that callosal division had apparently compromised the mechanisms sustaining feedback compensation for differences in the biomechanical limb properties. They also confirm and reinforce the idea that elaboration of the afferent message, aiming at controlling the phase of the movement association, needs the co-operation of both cerebral hemispheres.     

Identity matching and oddity learning in patients with moderate to severe Alzheimer-type dementia

Discrimination learning was investigated in patients with moderate to severe Alzheimer-type dementia (AD), comparing their performance with age-matched controls. Four AD patients were trained to criterion on identity matching and then shifted to the same task with novel stimuli. The AD patients showed no savings in learning to match novel stimuli, whereas a comparative group of four control subjects rapidly learned the novel matching discrimination, maintaining criterion performance on the transfer test. A second group of four patients was initially trained on oddity, taking a similar number of trials to reach criterion as the matching group. When these patients were subsequently shifted to the matching task with novel stimuli, they performed substantially worse than the first group of patients who had learned the matching task in the first stage. The lack of positive transfer in the shift between matching to matching suggests that the AD patients solved the identity-matching task on the basis of stimulus-response associations rather than a rule. The presence of negative transfer after shifting from oddity to matching may be explained by a pre-disposition to respond to a novel stimulus that is carried over into the matching task, but this warrants further investigation, as indicated in the discussion.     

The effects of circumferential air-splint pressure on flexor carpi radialis H-reflex in subjects without neurological deficits

The purposes of this study were to investigate the effects of circumferential pressure on flexor carpi radialis (FCR) H-reflex in subjects without neuromuscular deficits and to evaluate the skin's contribution to this effect. FCR H-reflex was assessed in 43 subjects by measuring the peak-to-peak amplitude change before, during, and after circumferential pressure was applied to the forearm. Twelve H-reflexes (H/M ratio: M = 25%, SD = 14) were recorded before pressure application to obtain a baseline value (H(baseline)) to which all data were compared. A pneumatic 15 to 20-cm air splint inflated to 51-60 mmHg provided the pressure around the forearm. H-reflex recordings were taken at 1, 3, and 5 min. during (H(pressure)) and after pressure application. A second smaller study (placebo), in which the air splint was inflated to 0 mmHg, was conducted in 5 subjects to ensure that changes in reflex amplitudes were not a result of cutaneous effects. Two types of responses were observed in the FCR H-reflex following pressure application. One group of subjects significantly increased in H-reflex amplitude while another group decreased in H-reflex amplitude when compared to H(baseline). Regression analysis found that H(max) explained 37.2% of the variance when controlling for H(baseline). Subjects with larger H(max) showed an increase in H(pressure) while subjects with lower H(max) showed decreases in H(pressure) The placebo study revealed no differences in H-reflex amplitude from baseline values, implying that skin stimulation from the air splint has no role in the effects observed. The dichotomous result indicates that pressure influences the upper extremity differently than it does the lower extremity in certain individuals. Clinicians, using circumferential pressure as a therapeutic modality to lower muscle activity of the upper extremity, need to be cognizant that pressure may have contrasting effects on their patients.     

Disrupting somatosensory processing impairs motor execution but not motor imagery

While motor imagery (MI) is thought to be ‘functionally equivalent’ with motor execution (ME), the equivalence of feedforward and feedback mechanisms between the two modalities is unexplored. Here, we tested the equivalence of these mechanisms between MI and ME via two experiments designed to probe the role of somatosensory processing (Exp 1), and cognitive processing (Exp 2). All participants were engaged in a previously established force-matching task adapted for MI. A reference force was applied (on scale of 1–10, with higher numbers indicative of greater force) to one index finger while participants matched the force with their opposite index finger via ME or MI (control conditions). Participants then rated the force on the same scale of 1–10. Exp 1: Participants (N = 27) performed the task with tactile stimulation (ME+TAC, MI+TAC) in addition to control conditions. Exp 2: Participants (N = 26) performed the task in dual-task conditions (ME+COG, MI+COG) in addition to control conditions. Results indicate that (Exp 1) tactile stimulation impaired performance in ME but not MI. Dual-task conditions (Exp 2) were not shown to impair performance in either practice modality. Findings suggest that while somatosensory processing is critical for ME, it is not for MI. Overall we indicate a functional equivalence between feedforward/back mechanisms in MI and ME may not exist.     

Functional decline in the early stages of Alzheimer's disease

At present most reports of functional decline in patients with Alzheimer's Disease (AD) are anecdotal, and few studies have objectively documented the course of the disease. This is a report of a 2-year follow-up of 15 AD patients characterized by mild functional impairment, and 22 age-, sex-, and education-matched control subjects. In a previous cross-sectional study of these 37 subjects and 16 AD patients with moderate functional impairment, we found that measures of memory and attention deficits accounted for much of the impairment observed in functional competence. The current longitudinal study found that these same initial assessments could be used to predict functional decline in the 15 mildly impaired patients. These patients were observed to decline to levels similar to those of the 16 moderate patients. In contrast, the control subjects exhibited little decline during the same period. These results both affirm that it is possible to diagnose AD in its mild form and demonstrate the validity of the initial diagnosis.     

Declining medical decision-making capacity in mild AD: a two-year longitudinal study

This is a report of a two-year longitudinal study comparing healthy older adult subjects (n = 15) and mild Alzheimer's disease (AD) patients (n = 20) using an objective performance measure of medical decision-making capacity (MDC). Capacity to consent to medical treatment was measured using the Capacity to Consent to Treatment Instrument (CCTI). The CCTI is a psychometric measure that tests MDC using a series of four core capacity standards: S1 (evidencing/communicating choice), S3 (appreciating consequences), S4 (providing rational reasons), and S5 (understanding treatment situation), and one experimental standard [S2] (making the reasonable treatment choice). For each standard, mild AD patients were assigned one of three capacity outcomes (capable, marginally capable, or incapable) based on cut-off scores derived from control group performance.At baseline, mild AD patients performed equivalently with controls on simple standards of evidencing a choice (S1) and making the reasonable choice ([S2]), but significantly below controls on complex standards of appreciation, reasoning, and understanding (S3, S4, and S5) (p < 0.02). Control performance was stable over time on all capacity standards. At one-year follow-up, the mild AD group did not show significant decline from baseline on any capacity standard. However, at two-year follow-up the mild AD group showed significant declines from baseline on the three complex standards (S3, S4, and S5) (p < 0.02), and a trend on one of the simple standards (S1). Over the two-year period, the proportion of marginally capable and incapable outcomes in the AD group increased substantially for four of the five standards (S1, S3, S4, and S5). Performance on [S2] remained stable over time in the AD group.We conclude that mild AD patients have impaired MDC at baseline, and demonstrate significant additional decline on complex consent abilities of appreciation, reasoning, and understanding over a two-year period. AD patients also show emerging impairment on the simple consent ability of evidencing choice at two-year follow-up. Capacity outcome data reflect similar declines over time for these four consent standards. The findings suggest the value of early assessment and regular monitoring at two-year intervals of MDC in patients with mild AD.     

Anxiety Symptoms as Predictors of Nursing Home Placement in Patients with Alzheimer's Disease

Anxiety symptoms are fairly common among patients with Alzheimer's Disease (AD). Such symptoms are likely to make patient care more problematic and, therefore, increase the risk of nursing home placement. Anxiety symptoms were evaluated on the basis of physician examinations, in conjunction with caregiver interviews, in 372 community-dwelling AD patients. Patients received annual follow-up for 1–12 years (M = 4.4). Patients who exhibited anxiety symptoms at baseline assessment were significantly more likely to enter nursing homes, regardless of initial cognitive status or other risks for institutionalization. There was a 15% increase in risk for each point on a 0–5 scale. This study supports the hypothesis that anxiety symptoms increase the risk of nursing home placement in patients with AD. Consequently, there is a need for better understanding of the causes of anxiety in AD and for the development of effective methods of assessment and treatment.     

An Associative Interpretation of the Indirect McCollough Effect

Following an induction procedure in which a coloured grid is alternated with a square of a complementary colour, subjects report colour after-effects on both the grid orientation present during induction and the orthogonal non-induced grid orientation. The after-effect reported on the induced grid orientation is called the McCollough effect (ME). The aftereffect reported on the non-induced grid orientation is called the indirect ME. There is evidence that the ME represents an instance of Pavlovian conditioning. The present results support a conditioning interpretation of the indirect ME and are inconsistent with interpretations of the indirect ME that attribute the phenomenon to special orthogonal coding mechanisms within the visual system.     

Cholinergic agents and the McCollough effect

The strength of the McCollough effect (ME), a pattern-contingent colour aftereffect, has been shown to be inversely related to acetylcholine, being significantly strengthened by (anticholinergic) scopolamine and weakened by (cholinergic) physostigmine delivered before adapting to the ME stimuli. The purpose of the present study was (i) to establish whether the effect of pre-adaptation scopolamine is linearly dose-dependent and (ii) to investigate the effects of scopolamine and physostigmine delivered between adaptation and testing. In experiment 1, ten healthy male volunteers who received placebo, or 0.6 mg, 1.2 mg, or 1.8 mg scopolamine before adapting to ME stimuli showed a significant linear dose-dependence over tests repeated from 10 to 70 min after adaptation. In experiment 2 twelve male volunteers adapted to ME stimuli and then received placebo, 1.2 mg oral scopolamine, or 0.75 mg subcutaneous physostigmine. On subsequent repeated testing, strength of the ME was increased by scopolamine and decreased by physostigmine relative to placebo. Both experiments were double-blind double-dummy repeated measures. These data support the view that the ME is a product of inhibitory mechanisms in the visual system rather than processes involved in associative learning.