Double dissociation of the roles of the left and right prefrontal cortices in anticipatory regulation of action

Recent actions can benefit or disrupt our current actions and the prefrontal cortex (PFC) is thought to play a major role in the regulation of these actions before they occur. The left PFC has been associated with overcoming interference from past events in the context of language production and working memory. The right PFC, and especially the right IFG, has been associated with preparatory inhibition processes. But damage to the right PFC has also been associated with impairment in sustaining actions in motor intentional disorders. Moreover, bilateral dorsolateral PFC has been associated with the ability to maintain task-sets, and improve the performance of current actions based on previous experience. However, potential hemispheric asymmetries in anticipatory regulation of action have not yet been delineated. In the present study, patients with left (n=7) vs. right (n=6) PFC damage due to stroke and 14 aged- and education-matched controls performed a picture naming and a verbal Simon task (participants had to say "right" or "left" depending on the color of the picture while ignoring its position). In both tasks, performance depended on the nature of the preceding trial, but in different ways. In the naming task, performance decreased if previous pictures were from the same rather than from different semantic categories (i.e., semantic interference effect). In the Simon task, performance was better for both compatible (i.e., response matching the position of the stimulus) and incompatible trials when preceded by a trial of the same compatibility (i.e. Gratton effect) relative to sequential trials of different compatibility. Left PFC patients were selectively impaired in picture naming; they had an increased semantic interference effect compared to both right PFC patients and aged-matched controls. Conversely, right PFC patients were selectively impaired in the Simon task compared to controls or left PFC patients; they showed no benefit when sequential trials were compatible (cC vs. iC trials) or a decreased Gratton effect. These results provide evidence for a double dissociation between left and right PFC in the anticipatory regulation of action. Our results are in agreement with a preponderant role of the left PFC in overcoming proactive interference from competing memory representations and provide evidence that the right PFC, plays a role in sustaining goal-directed actions consistent with clinical data in right PFC patients with motor intentional disorders.

Decreased white matter integrity in late-myelinating fiber pathways in Alzheimer's disease supports retrogenesis

The retrogenesis model of Alzheimer's disease (AD) posits that white matter (WM) degeneration follows a pattern that is the reverse of myelogenesis. Using diffusion tensor imaging (DTI) to test this model, we predicted greater loss of microstructural integrity in late-myelinating WM fiber pathways in AD patients than in healthy older adults, whereas differences in early-myelinating WM fiber pathways were not expected. We compared 16 AD patients and 14 demographically-matched healthy older adults with a whole-brain approach via tract-based spatial statistics (TBSS), and a region of interest (ROI) approach targeting early-myelinating (posterior limb of internal capsule, cerebral peduncles) and late-myelinating (inferior longitudinal fasciculus [ILF], superior longitudinal fasciculus [SLF]) fiber pathways. Permutation-based voxelwise analysis supported the retrogenesis model. There was significantly lower fractional anisotropy (FA) in AD patients compared to healthy older adults in late-myelinating but not early-myelinating pathways. These group differences appeared to be driven by loss of myelin integrity based on our finding of greater radial diffusion in AD than in healthy elderly. ROI analyses were generally in agreement with whole-brain findings, with significantly lower FA and increased radial diffusion in the ILF in the AD group. Consistent with the retrogenesis model, AD patients showed demonstrable changes in late-myelinating WM fiber pathways. Given greater change in the ILF than the SLF, wallerian degeneration secondary to cortical atrophy may also be a contributing mechanism. Knowledge of the pattern of WM microstructural changes in AD and its underlying mechanisms may contribute to earlier detection and intervention in at-risk groups.

Neuropsychological functioning following a spinal cord injury

Studies indicate that 10-60% of the spinal cord injury (SCI) population retains residual cognitive deficits following the injury. However, previous studies have not used a comprehensive neuropsychological battery and/or a well-matched control group. In addition, no study has determined if cognitive deficits continue more than one year after injury. The present study addressed these limitations by comparing the performance of a chronic SCI group (Mean = 17 years post-injury) and a well-matched control group in four cognitive areas. Memory, visuospatial skills, attention/executive functioning, and processing speed were assessed. Results from a discriminant function analysis indicated that information processing speed best differentiated between the SCI and control groups. Twenty-nine percent of the SCI group performed 1 to 2 standard deviations below the control group mean. These results could not be attributed to psychological status or history of alcohol consumption. The findings emphasize the importance of neuropsychological evaluation after SCI.

Ideomotor limb apraxia in Huntington's disease: implications for corticostriate involvement

Ideomotor limb apraxia, a disorder of goal-directed movement, has been attributed to lesions in the frontal and parietal lobes, but the role of subcortical structures is less certain. In order to determine its prevalence in a disorder affecting the basal ganglia and corticostriatal connections, we examined imitation of hand gestures in Huntington's disease (HD) patients. We also assessed the relationship between apraxia and cognitive and motor dysfunction in an effort to better understand the neural underpinnings of apraxia in HD. If damage restricted to the basal ganglia produces ideomotor limb apraxia, then we would expect to find evidence of apraxia in patients who were early in the disease course when selective striatal damage is most common. Such a pattern, however, was not found in our sample. Instead, patients with greater neurological impairment and with a longer duration of disease were more likely than less affected patients to demonstrate apraxia. Apraxia was not related to severity of chorea, but was associated with greater impairment in eye movements, voluntary movements, and verbal fluency. These findings suggest that apraxia in HD results from damage to the corticostriate pathways and the basal ganglia rather than from damage restricted to the basal ganglia.

Neural representations of skilled movement

The frontal and parietal cortex are intimately involved in the representation of goal-directed movements, but the crucial neuroanatomical sites are not well established in humans. In order to identify these sites more precisely, we studied stroke patients who had the classic syndrome of ideomotor limb apraxia, which disrupts goal-directed movements, such as writing or brushing teeth. Patients with and without limb apraxia were identified by assessing errors imitating gestures and specifying a cut-off for apraxia relative to a normal control group. We then used MRI or CT for lesion localization and compared areas of overlap in those patients with and without limb apraxia. Patients with ideomotor limb apraxia had damage lateralized to a left hemispheric network involving the middle frontal gyrus and intraparietal sulcus region. Thus, the results revealed that discrete areas in the left hemisphere of humans are critical for control of complex goal-directed movements.

American Board of Clinical Neuropsychology special presentation: The American Board of Clinical Neuropsychology (ABCN), 2000 update

This paper updates neuropsychologists on the process of obtaining board certification in clinical neuropsychology through the American Board of Clinical Neuropsychology (ABCN), a specialty board operating under the auspices of the American Board of Professional Psychology (ABPP). At this time, the ABPP and ABCN have certified 406 clinical neuropsychologists, which makes it the largest board-certification organization in clinical neuropsychology. This article details the advantages of board certification through the ABCN and the four steps which must be passed in order to obtain board certification. These steps are: credential review, written examination, work sample, and oral examination.

Neural underpinnings of temporal processing: a review of focal lesion, pharmacological, and functional imaging research

The mechanisms by which the brain times events and stores them in memory for later use is increasingly of interest to neuroscientists. There are a variety of neurological disorders in which skilled behaviors are not coordinated and appear less than fluent, which may suggest a disorder in temporal processing. In this review, two influential models are described which suggest timing deficits may be due to impairments in a timekeeping mechanism or various nontemporal processes such as motor implementation, memory, and attention. We then review focal lesion, pharmacological, and functional imaging approaches to understanding the neural underpinnings of temporal processing. Converging findings from these approaches provide support for the role of the basal ganglia in timekeeping operations. Likewise, focal lesion and some functional imaging studies are compatible with a timekeeping role of the cerebellum, though specific regions within the cerebellum that control timing operations have not been identified. In contrast, the results from recent focal lesion research suggests the right middle-frontal and inferior-parietal cortices comprise a pathway that supports attention and working memory operations, which are crucial for timing. Functional imaging data provide some converging evidence for this proposal. Functional imaging work also indicates that a right superior-temporal inferior-frontal pathway sometimes aids timing through subvocal nonlinguistic rehearsal processes. These distributed pathways maintain timekeeping operations in working memory and store representations of temporal events, which is crucial for skilled performance.

Specialized neural systems underlying representations of sequential movements

The ease by which movements are combined into skilled actions depends on many factors, including the complexity of movement sequences. Complexity can be defined by the surface structure of a sequence, including motoric properties such as the types of effectors, and by the abstract or sequence-specific structure, which is apparent in the relations amongst movements, such as repetitions. It is not known whether different neural systems support the cognitive and the sensorimotor processes underlying different structural properties of sequential actions. We investigated this question using whole-brain functional magnetic resonance imaging (fMRI) in healthy adults as they performed sequences of five key presses involving up to three fingers. The structure of sequences was defined by two factors that independently lengthen the time to plan sequences before movement: the number of different fingers (1-3; surface structure) and the number of finger transitions (0-4; sequence-specific structure). The results showed that systems involved in visual processing (extrastriate cortex) and the preparation of sensory aspects of movement (rostral inferior parietal and ventral premotor cortex (PMv)) correlated with both properties of sequence structure. The number of different fingers positively correlated with activation intensity in the cerebellum and superior parietal cortex (anterior), systems associated with sensorimotor, and kinematic representations of movement, respectively. The number of finger transitions correlated with activation in systems previously associated with sequence-specific processing, including the inferior parietal and the dorsal premotor cortex (PMd), and in interconnecting superior temporal-middle frontal gyrus networks. Different patterns of activation in the left and right inferior parietal cortex were associated with different sequences, consistent with the speculation that sequences are encoded using different mnemonics, depending on the sequence-specific structure. In contrast, PMd activation correlated positively with increases in the number of transitions, consistent with the role of this area in the retrieval or preparation of abstract action plans. These findings suggest that the surface and the sequence-specific structure of sequential movements can be distinguished by distinct distributed systems that support their underlying mental operations.

Spatial deficits in ideomotor limb apraxia. A kinematic analysis of aiming movements

Ideomotor limb apraxia is a classic neurological disorder manifesting as a breakdown in co-ordinated limb control with spatiotemporal deficits. We employed kinematic analyses of simple aiming movements in left hemisphere-damaged patients with and without limb apraxia and a normal control group to examine preprogramming and response implementation deficits in apraxia. Damage to the frontal and parietal lobes was more common in apraxics, but neither frontal nor parietal damage was associated with different arm movement deficits. Limb apraxia was associated with intact preprogramming but impaired response implementation. The response implementation deficits were characterized by spatial but not temporal deficits, consistent with decoupling of spatial and temporal features of movement in limb apraxia. While the apraxics' accuracy was normal when visual feedback was available, it was impaired when visual feedback of either target location or hand position was unavailable. This finding suggests that ideomotor limb apraxia is associated with disruption of the neural representations for the extrapersonal (spatial location) and intrapersonal (hand position) features of movement. The non-apraxic group's normal kinematic performance demonstrates that the deficits demonstrated in the apraxic group are not simply a reflection of left hemisphere damage per se.

Temporal processing in the basal ganglia

This study investigated the role of the basal ganglia in timing operations. Nondemented, medicated Parkinson's disease (PD) patients and controls were tested on 2 motor-timing tasks (paced finger tapping at a 300- or 600-ms target interval), 2 time perception tasks (duration perception wherein the interval between the standard tone pair was 300 or 600 ms), and 2 tasks that controlled for the auditory processing (frequency perception) demands of the time perception task and the movement rate (rapid tapping) in the motor-timing task. Using A.M. Wing and A.B. Kristofferson's (1973) model, the total variability in motor timing was partitioned into a clock component, which reflects central timekeeping operations, and a motor delay component, which estimates random variability due to response implementation processes. The PD group was impaired at both target intervals of the time perception and motor-timing tasks. Impaired motor timing was due to elevated clock but not motor delay variability. The findings implicate the basal ganglia and its thalamocortical connections in timing operations.

Cortical networks underlying mechanisms of time perception

Precise timing of sensory information from multiple sensory streams is essential for many aspects of human perception and action. Animal and human research implicates the basal ganglia and cerebellar systems in timekeeping operations, but investigations into the role of the cerebral cortex have been limited. Individuals with focal left (LHD) or right hemisphere (RHD) lesions and control subjects performed two time perception tasks (duration perception, wherein the standard tone pair interval was 300 or 600 msec) and a frequency perception task, which controlled for deficits in time-independent processes shared by both tasks. When frequency perception deficits were controlled, only patients with RHD showed time perception deficits. Time perception competency was correlated with an independent test of switching nonspatial attention in the RHD but not the LHD patients, despite attention deficits in both groups. Lesion overlays of patients with RHD and impaired timing showed that 100% of the patients with anterior damage had lesions in premotor and prefrontal cortex (Brodmann areas 6, 8, 9, and 46), and 100% with posterior damage had lesions in the inferior parietal cortex. All LHD patients with normal timing had damage in these same regions, whereas few, if any, RHD patients with normal timing had similar lesion distributions. These results implicate a right hemisphere prefrontal-inferior parietal network in timing. Time-dependent attention and working memory functions may contribute to temporal perception deficits observed after damage to this network.

Temporal processing in the basal ganglia

This study investigated the role of the basal ganglia in timing operations. Nondemented, medicated Parkinson's disease (PD) patients and controls were tested on 2 motor-timing tasks (paced finger tapping at a 300- or 600-ms target interval), 2 time perception tasks (duration perception wherein the interval between the standard tone pair was 300 or 600 ms), and 2 tasks that controlled for the auditory processing (frequency perception) demands of the time perception task and the movement rate (rapid tapping) in the motor-timing task. Using A.M. Wing and A.B. Kristofferson's (1973) model, the total variability in motor timing was partitioned into a clock component, which reflects central timekeeping operations, and a motor delay component, which estimates random variability due to response implementation processes. The PD group was impaired at both target intervals of the time perception and motor-timing tasks. Impaired motor timing was due to elevated clock but not motor delay variability. The findings implicate the basal ganglia and its thalamocortical connections in timing operations.

Profiles of cognitive functioning in chronic spinal cord injury and the role of moderating variables

A traumatic spinal cord injury (SCI) is accompanied by a documented moderate to severe head injury in significant numbers of SCI patients. In a previous study (Dowler et al., 1995), cognitive deficits were found in 41% of the SCI individuals who were studied with a chronic injury from a traumatic event. The present study investigated whether clinically useful subtypes of normal and impaired cognition could be identified in a chronic (M = 17 years postinjury) SCI sample using a cluster analysis of neuropsychological test performance. A battery of 16 neuropsychological tests was administered to 91 SCI patients and 75 control participants. Composite scores, reflecting performance in different cognitive domains, were derived from a factor analysis of the battery, and these scores were then used in the cluster analysis. A six-cluster solution generated the most distinct and clinically relevant SCI group profiles. Two of the cognitive profiles were characterized by normal functioning in all cognitive domains, but they were distinguished by differences in performance levels. The remaining four SCI groups (60% of the sample) showed clinically significant deficits in one or more cognitive domains, with different groups showing moderate attention and processing speed deficits, mild deficits in processing speed, executive processing difficulties, or moderate memory impairments. Though age and premorbid intellectual ability were strong predictors of the cognitive profiles of some SCI groups, when these factors were controlled, the findings suggested that the patterns of cognitive impairment were likely due to a potential concomitant head injury.

Distributed neural systems underlying the timing of movements

Timing is essential to the execution of skilled movements, yet our knowledge of the neural systems underlying timekeeping operations is limited. Using whole-brain functional magnetic resonance imaging, subjects were imaged while tapping with their right index finger in synchrony with tones that were separated by constant intervals [Synchronization (S)], followed by tapping without the benefit of an auditory cue [Continuation (C)]. Two control conditions followed in which subjects listened to tones and then made pitch discriminations (D). Both the S and the C conditions produced equivalent activation within the left sensorimotor cortex, the right cerebellum (dorsal dentate nucleus), and the right superior temporal gyrus (STG). Only the C condition produced activation of a medial premotor system, including the caudal supplementary motor area (SMA), the left putamen, and the left ventrolateral thalamus. The C condition also activated a region within the right inferior frontal gyrus (IFG), which is functionally interconnected with auditory cortex. Both control conditions produced bilateral activation of the STG, and the D condition also activated the rostral SMA. These results suggest that the internal generation of precisely timed movements is dependent on three interrelated neural systems, one that is involved in explicit timing (putamen, ventrolateral thalamus, SMA), one that mediates auditory sensory memory (IFG, STG), and another that is involved in sensorimotor processing (dorsal dentate nucleus, sensorimotor cortex).

Cognitive-motor learning in Parkinson's disease

Procedural learning deficits are common in Parkinson's disease (PD), but contradictory results have been reported in rotary pursuit learning. This article compared rotary pursuit learning in 2 nondemented PD groups and 2 normal control (NC) groups, using a between-subjects group design in which 3 rotation speeds were presented either randomly or in blocks. The pattern of learning differed between the randomized and the blocked conditions in the NC, but not in the PD groups. Learning was impaired in the PD group in the random condition only. Memory, visuospatial, or executive skills were not associated with the PD group's poorer learning in the randomized context. Results show that procedural learning deficits are not universal with basal ganglia abnormalities but rather depend on the specific cognitive requirements of the learning context.

Cognitive-motor learning in Parkinson's disease

Procedural learning deficits are common in Parkinson's disease (PD), but contradictory results have been reported in rotary pursuit learning. This article compared rotary pursuit learning in 2 nondemented PD groups and 2 normal control (NC) groups, using a between-subjects group design in which 3 rotation speeds were presented either randomly or in blocks. The pattern of learning differed between the randomized and the blocked conditions in the NC, but not in the PD groups. Learning was impaired in the PD group in the random condition only. Memory, visuospatial, or executive skills were not associated with the PD group's poorer learning in the randomized context. Results show that procedural learning deficits are not universal with basal ganglia abnormalities but rather depend on the specific cognitive requirements of the learning context.

Nutritional status and cognitive functioning in a normally aging sample: a 6-y reassessment

Associations between nutritional status and cognitive performance were examined in 137 elderly (aged 66-90 y) community residents. Participants were well-educated, adequately nourished, and free of significant cognitive impairment. Performance on cognitive tests in 1986 was related to both past (1980) and concurrent (1986) nutritional status. Several significant associations (P < 0.05) were observed between cognition and concurrent vitamin status, including better abstraction performance with higher biochemical status and dietary intake of thiamine, riboflavin, niacin, and folate (rs = 0.19-0.29) and better visuospatial performance with higher plasma ascorbate (r = 0.22). Concurrent dietary protein in 1986 correlated significantly (rs = 0.25-0.26) with memory scores, and serum albumin or transferrin with memory, visuospatial, or abstraction scores (rs = 0.18-0.22). Higher past intake of vitamins E, A, B-6, and B-12 was related to better performance on visuospatial recall and/or abstraction tests (rs = 0.19-0.28). Use of self-selected vitamin supplements was associated with better performance on a difficult visuospatial test and an abstraction test. Although associations were relatively weak in this well-nourished and cognitively intact sample, the pattern of outcomes suggests some direction for further research on cognition-nutrition associations in aging.

Hemispheric asymmetry of movement

Studies in brain-damaged patients indicate that the left hemisphere in right-handers is specialized for controlling cognitive-motor tasks in both arms. Recent functional imaging data support this conclusion, with the finding that ipsilateral, as well as contralateral, movements activate the left, but not the right, motor cortex or association areas of either hemisphere. Future studies must aspire to identify the mechanisms for this asymmetry.

Recovery of simple motor skills after head injury

The performance of 40 head-injured patients (HI) without peripheral upper body injuries and 88 normal controls were compared on finger tapping and grip strength 1 month and 1 year after injury. The HI group demonstrated deficits on both tasks 1 month after injury, but only finger tapping was impaired 1 year postinjury. While grip strength differentially improved in the HI group from 1 month to 1 year, finger tapping improved similarly in both groups. The pattern of results was similar when a subset of 25 HI patients without any evidence of focal lesions were examined. These results demonstrate (1) motor deficits are present 1 year after injury even in a sample of predominantly mild head-injury patients, (2) grip strength is more sensitive to recovery in the first year after head injury, and (3) finger tapping continues to be impaired 1 year after head injury possibly due to its speed requirements.

Methylmercury poisoning: long-term clinical, radiological, toxicological, and pathological studies of an affected family

For 3 months in 1969 a family in the United States that included a pregnant mother consumed pork containing methylmercury. Children, aged 20, 13, and 8 years and a neonate, developed severe neurological signs. Twenty-two years later, the 2 oldest had cortical blindness or constricted visual fields, diminished hand proprioception, choreoathetosis, and attentional deficits. Magnetic resonance images showed tissue loss in the calcarine and parietal cortices and cerebellar folia. The youngest had quadriplegia, blindness, and severe mental retardation until their deaths. The brain of the 8-year-old who died at age 30 showed cortical atrophy, neuronal loss, and gliosis, most pronounced in the paracentral and parietooccipital regions. The total mercury level in formalin-fixed, left occipital cortex was 1,974 ng/gm as measured by atomic absorption. Regional brain mercury levels correlated with extent of brain damage. A control patient had 38.5 ng of mercury/gm in the occipital cortex. Systemic organs in the patient and a control subject had comparable mercury levels. In mercury-intoxicated rats, we found that only 5 to 10% of total brain mercury was lost by formalin fixation. Brain inorganic mercury in the patient ranged from 82 to 100%. Since inorganic mercury crosses the blood-brain barrier poorly, biotransformation of methyl to inorganic mercury may have occurred after methylmercury crossed the blood-brain barrier, accounting for its persistence in brain and causing part of the brain damage.

Effects of aging on planning and implementing arm movements

In Experiments 1 and 2, aiming movements were performed with and without visual feedback in young and elderly adults. The initial (acceleration and deceleration phases) and secondary movement components were analyzed. Although deceleration phase accuracy decreased without visual feedback in both age groups, accuracy diminished as movement amplitude increased only in the elderly. This suggested that the elderly were more dependent on visual feedback to modify motor programs for longer duration movements. Velocity also increased less with increasing amplitude and target size in the elderly, which was related to impaired preprogramming (acceleration phase) and implementation (deceleration phase) of higher forces. This conclusion was confirmed directly in Experiment 2 because only the deceleration phase was affected by the removal of visual feedback of arm position when availability of visual information could not be predicted before movement.

Limb-sequencing deficits after left but not right hemisphere damage

The performance of right and left hemisphere stroke patients was compared to normal control groups on a task where subjects alternately hit two targets which varied in size from 0.5 to 6.5 cm. The stroke patients used the arm ipsilateral to damage, and the control groups used the same arm as their respective stroke group. Lesion size and location were similar for the two stroke groups. No deficits were found for the right hemisphere stroke group. The left stroke group's tapping speed was not slower at the smallest target, but became progressively slower relative to the control group's as target size increased. Variability in tapping speed increased as target size increased for all except the left stroke group. While the entire left stroke group was as accurate as their controls, the apraxic, but not nonapraxic, patients made more errors on smaller targets only. Two explanations for these findings both emphasize the left hemisphere's special role in motor programming; one focuses upon its dominance for movements which are independent of sensory feedback and the other emphasizes its specialization for processing rapid temporal information.

Effects of aging on planning and implementing arm movements

In Experiments 1 and 2, aiming movements were performed with and without visual feedback in young and elderly adults. The initial (acceleration and deceleration phases) and secondary movement components were analyzed. Although deceleration phase accuracy decreased without visual feedback in both age groups, accuracy diminished as movement amplitude increased only in the elderly. This suggested that the elderly were more dependent on visual feedback to modify motor programs for longer duration movements. Velocity also increased less with increasing amplitude and target size in the elderly, which was related to impaired preprogramming (acceleration phase) and implementation (deceleration phase) of higher forces. This conclusion was confirmed directly in Experiment 2 because only the deceleration phase was affected by the removal of visual feedback of arm position when availability of visual information could not be predicted before movement.

Skill learning in the elderly: diminished implicit and explicit memory for a motor sequence

Explicit and implicit memory for a cognitive-motor sequence was studied in elderly and young adults. Implicit memory was examined in a serial reaction-time paradigm in which sequences of hand postures repeated cyclically, then shifted to random sequences. Two control groups received random sequences throughout. Movement times (MTs) across the first 4 blocks did not improve more in the elderly-repeated than in the elderly-random group. In contrast, the young-repeated group showed greater improvement in MT across these blocks than the young-random group. MT was less affected in the elderly than in the young by shifts between repeated and random sequences, indicating impaired implicit memory. Explicit memory, which was assessed by free recall and cued recall, also was impaired in the elderly. Diminished implicit memory in the elderly could not be explained solely by the possible intrusion of conscious recollection strategies.

Introduction to the special section on the emotional concomitants of brain damage

The purpose of this introduction is to emphasize the theoretical and clinical implications of studying emotion after brain damage. Theoretically, it is one way of elucidating critical neural substrates of emotion and the interaction of cognitive and noncognitive determinants. Clinically, the cognitive and other behavioral changes associated with certain types of brain damage may make traditional methods of assessing emotion inaccurate. This special section is designed to review current knowledge regarding these issues and to emphasize their theoretical and clinical importance.

Motor sequencing with left hemisphere damage. Are some cognitive deficits specific to limb apraxia?

Sixteen left-hemisphere stroke patients, who were apraxic or nonapraxic, and 17 control subjects performed sequences of hand postures that varied in the number of different postures (repetitive and heterogeneous) and sequence length (one to five). Performance of the left hand (ipsilateral to stroke) was compared with a control group using the left hand. All stroke patients had slower reaction times and were slower to execute single hand postures, but the apraxic group was not slower than the nonapraxic group. Both the apraxic and the nonapraxic groups had similar problems scheduling or timing motor programs for both sequence types such that inter-response times were more affected by sequence length than the control group. However, only the apraxic group showed abnormalities in preprogramming heterogeneous sequences. The apraxic group also made more errors and had longer movement times (MTs) than for the other groups, but only for heterogeneous sequences containing more than three hand postures. The nonapraxic group did not show slower MTs or greater errors, regardless of the type or the length of sequences. These results suggested deficits in encoding, generating single movements and in scheduling or timing a series of actions which generally attributable to left hemisphere damage. However, abnormalities in temporal organization processes prior to and during movement were specific to apraxia. The dissociation between the two stroke groups on some but not all aspects of sequencing has implications for different cognitive mechanisms supporting motor sequencing.

Introduction to the Special Section on the Emotional Concomitants of Brain Damage

The purpose of this introduction is to emphasize the theoretical and clinical implications of studying emotion after brain damage. Theoretically, it is one way of elucidating critical neural substrates of emotion and the interaction of cognitive and noncognitive determinants. Clinically, the cognitive and other behavioral changes associated with certain types of brain damage may make traditional methods of assessing emotion inaccurate. This special section is designed to review current knowledge regarding these issues and to emphasize their theoretical and clinical importance.

Skill learning in the elderly: Diminished implicit and explicit memory for a motor sequence

Explicit and implicit memory for a cognitive-motor sequence was studied in elderly and young adults. Implicit memory was examined in a serial reaction-time paradigm in which sequences of hand postures repeated cyclically, then shifted to random sequences. Two control groups received random sequences throughout. Movement times (MTs) across the first 4 blocks did not improve more in the elderly-repeated than in the elderly-random group. In contrast, the young-repeated group showed greater improvement in MT across these blocks than the young-random group. MT was less affected in the elderly than in the young by shifts between repeated and random sequences, indicating impaired implicit memory. Explicit memory, which was assessed by free recall and cued recall, also was impaired in the elderly. Diminished implicit memory in the elderly could not be explained solely by the possible intrusion of conscious recollection strategies.

Hearing and cognition in the elderly. New findings and a review of the literature

The purpose of this study was to determine the relationship between hearing status and cognitive status initially and at 5-year follow-up in a cohort of healthy elderly men and women and to relate the results to published reports on this topic. Volunteers older than 60 years with no major illnesses and taking no long-term prescription medications were examined. Baseline testing of hearing and cognition was performed in 224 subjects; 112 subjects underwent cognitive testing at 5-year follow-up. Hearing was measured by the Speech Perception in Noise test; cognition was measured by two parts of the Wechsler Memory Scale and by the Jacobs Cognitive Screening Test, an oral screening instrument. At baseline there were small correlations between hearing acuity and memory scores, but these disappeared after adjustment for age and gender. Analysis of follow-up memory and cognitive screening test scores in relation to baseline hearing ability showed no correlation between hearing at entry and cognitive function at 5 years. In addition, baseline hearing level did not predict change in memory or cognitive screening test scores during the follow-up period. The power of the study was 90% to detect a correlation of .30 between measures of hearing and cognition. There was no evidence for a major effect of hearing acuity on cognitive function over time in this group of healthy elderly. Review of published studies suggests that hearing ability is related to cognitive status in demented subjects, but there is little to suggest that in the normal elderly, hearing impairment leads to cognitive decline.

Sequencing in Parkinson's disease. Abnormalities in programming and controlling movement

Central programming deficits in Parkinson's disease (PD) were studied in two reaction time (RT) experiments. In Experiment 1, PD patients and controls performed sequences of hand postures that varied in length, the number of different postures (repetitive vs heterogeneous), and the delay interval before movement. Before movement, the PD group planned repetitive movements like controls whereas for heterogeneous sequences RT increased less with sequence length for the PD group, implying less preprogramming. The interresponse time (IRT) data from repetitive sequences showed that the PD group had difficulty controlling movement such that IRTs were faster when sequences were longer, thus allowing more time to schedule the termination of the sequence during the course of movement. For heterogeneous sequences, the PD group made more errors and were slower than controls when changing hand postures, suggesting a deficit in switching between different responses. While RT decreased with a longer delay similarly for both groups, IRT1 continued to improve only for the PD group but similarly for both types of sequences, suggesting a deficit specific to programming the first response. In Experiment 2, subjects made decisions about the number of different hand postures contained within a sequence. PD patients' decision times improved more with a longer delay only for heterogeneous sequences, suggesting a problem in identifying the number of different hand postures. The results have implications for levels of motor dysfunction in PD which emphasize the influence of sequence length and complexity.

Hemispheric specialization for motor sequencing: abnormalities in levels of programming

Left and right hemisphere stroke patients and control subjects performed sequences of hand postures which varied in complexity (repetitive and heterogeneous) and length (one to five). Performance in the hand ipsilateral to the stroke was compared to a control group using the same hand. Neither stroke group had problems preprogramming sequences prior to movement. The only deficit seen for the right hemisphere group was a greater difference in movement time (MT) between heterogeneous and repetitive sequences relative to controls, regardless of sequence length. This suggested right hemisphere damage results in subtle timing but not error deficits on more complex movements, perhaps due to increased external spatial demands. The left hemisphere group was slower to execute single postures, and had difficulty scheduling motor programs for repetitive and heterogeneous movements such that inter-response times (IRTs) were more affected by sequence length than for controls. Left hemisphere patients also made more errors on heterogeneous sequences as they increased in length, and the difference in MTs between repetitive and heterogeneous sequences increased more with increasing length relative to their control group. These results suggested the left hemisphere plays a role in controlling single postures, in scheduling motor programs during repetitive and heterogeneous movements, and in processes related to sequential ordering.

Procedural memory in Parkinson's disease: impaired motor but not visuoperceptual learning

A current model proposes that memory consists of two functionally separate systems that have different neurological substrates. Declarative memory appears to be dependent on the diencephalic medial temporal lobe system whereas some speculate that the basal ganglia may be a neurological substrate for procedural memory. This study tested the role of the basal ganglia in regulating different types of procedural skills by comparing performance on a motor and a visuoperceptual skill learning task. Twenty Parkinson's (PD) patients and 20 normal control subjects performed two procedural learning tasks (rotary pursuit and mirror reading) and one declarative learning task (paired associates) over 3 days. The results showed that PD patients were not impaired on mirror reading or paired associate learning. On rotary pursuit, performance levels on day 1 were similar between groups, but the PD group showed less improvement across days than controls. However, only patients with more advanced symptoms of PD showed impaired rotary pursuit learning, and this could not be attributed directly to deficits in primary motor or general cognitive function. These findings suggest that the underlying processes/procedures for procedural learning are specific to the task, and are supported by different neuroanatomical systems.

Clinical significance of MRI white matter lesions in the elderly

The clinical relevance of white matter hyperintensities (WMH) seen on MRIs of elderly individuals is controversial. To resolve this issue, we performed MRI and neuropsychological testing on 46 healthy participants in the longitudinal Aging Process Study at the University of New Mexico. We graded the MRIs for severity of WMH using a scale tested on an elderly patient population. We found that 22% of normal subjects had moderate lesions and 9% had severe lesions. All subjects had normal neurologic examination findings and were within normal limits on a battery of neuropsychological tests. Neuropsychological performance decreased and the severity of WMH increased with age. However, when the data were corrected for age, there was no correlation between neuropsychological function and the presence of WMH. We conclude that white matter changes in the elderly by themselves are of doubtful clinical significance.

The role of the hemispheres in closed loop movements

The purpose of these experiments was to determine if the two hemispheres play different roles in controlling closed loop movements. Subjects were asked to move to a narrow or wide target in the left or right hemispace. Reaction time (RT) was faster for the left arm of normals, only in the right hemispace, but there were no differences between arms in movement execution. Right but not left hemisphere stroke (CVA) patients showed longer RTs for the contralateral but not ipsilateral arm. The right CVA group's ipsilateral movement, especially to narrow targets was less accurate. The left CVA group's RT did not benefit from advanced information, but ipsilateral movement execution was normal. These results were discussed in terms of inter- as well as intrahemispheric control of programming and execution of closed loop movements.

Hemispheric control of the initial and corrective components of aiming movements

This study examined whether the left and right hemispheres play differential roles in controlling the initial and corrective components of aiming movements. A simple aiming task was administered to 31 normal control subjects and 29 unilateral stroke patients (14 with right hemisphere damage and 15 with left hemisphere damage). Movement amplitude was varied (25, 64 and 100 mm) and reaction time, movement time and accuracy were measured. Through a trajectory analysis, initial and corrective movements were separated. The stroke patients performed the task with their ipsilateral arm which was compared to the normal controls' right or left are performance. Regardless of the movement amplitude the left hemisphere group's reaction time was slower, and the execution of the initial movement component was less accurate than controls. No performance deficits were found on corrective movements. Performance was not impaired for the right hemisphere group on any measures. These results are discussed in terms of the hemispheres' possible roles in controlling movements which are largely open or closed loop.

Wisconsin Card Sort Test performance in a healthy elderly population

A 64-card version of the Wisconsin Card Sort Test (WCST) was administered to 5 groups (n = 95), aged 17 to 25, 64 to 69, 70 to 74, 75 to 79 and 80 to 87 years. The elderly groups were chosen for their lack of medical problems in order to determine if previously reported age-related deficits were due to chronic medical problems or to aging per se. The resulting pattern of means showed statistically significant differences only for number of categories attained and total number of errors. For both variables, the 80- to 87-year-old group performed more poorly than the 64- to 69-year-old group. These results, although consistent with previous findings suggestive of frontal lobe vulnerability in old age, indicate that deterioration is less marked for a healthy elderly population.

The effects of task complexity on motor performance in left and right CVA patients

The effects of task complexity on movement ipsilateral to lesion were examined using the Fitts tapping task [Fitts, P.M., J. exp. Psychol. 47, 381-391, 1954]. Subjects were required to rapidly tap two targets, which were 1 or 4 cm wide. Twenty controls and ten left hemisphere and nine right hemisphere stroke patients were studied. Only the left hemisphere group showed significant deficits with greater impairment found in the wide target condition. Quantified CT scan analyses indicated lesion volume was similar between CVA groups, but the left hemisphere group's lesions were more anterior. The results are discussed in terms of inter- and intrahemispheric roles in open and closed loop movements.

The different types of limb apraxia errors made by patients with left vs. right hemisphere damage

Limb apraxia errors were compared among normal controls and right- or left-hemisphere-damaged patients as they imitated gestures with the ipsilateral hand. Both brain-damaged groups made similar errors on nonrepresentative and representative/intransitive movements. In contrast for pretended object use movements (transitive), the left-hemisphere-damaged group made more arm position and classical body-part-as-object errors while the right hemisphere group made as many partial errors and more less-primitive, body-part-as-object errors than the left-hemisphere-damaged group. These results help explain why a certain percentage of right-hemisphere-damaged patients are labeled apraxic, but also suggest that the left hemisphere is more important for integrating intrapersonal space and the "representation" of extrapersonal space.

The relationship of limb apraxia severity to motor and language deficits

Ipsilateral motor and symbolic/linguistic skills were examined in normals and three left hemisphere damaged groups with no, mild, or moderate-severe limb apraxia. When the two apraxic groups were pooled they demonstrated poorer response inhibition and reading relative to the nonapraxic group. There were no significant group differences on motor or language tasks when the three brain damaged groups were separately compared. These results indicate there is a limited relationship between limb apraxia and some motor and linguistic skills, but the relationship was not greater for motor than linguistic skills.

Botulism and memory

Although botulinum toxin is thought not to affect the human CNS, previous studies have not examined those behaviors, such as memory, that have been shown to be dependent on central acetylcholine transmission. In eight patients with type A botulism, subjective analysis, bedside memory testing, and formal memory testing with Hebb's verbal sequencing test, Corsi's nonverbal sequencing test, and Buschke's verbal serial list learning test failed to demonstrate impairment in immediate and recent memory. Botulism severe enough to block peripheral nicotinic and muscarinic cholinergic transmission does not block those central cholinergic synapses involved in memory.

The effect of symptom duration on cognitive and motor performance in parkinsonism

Neuropsychologic test performance was examined in a normal control group and in three groups of Parkinson disease patients, with symptoms for 2 years or less, for 3 to 5 years, or for 6 to 15 years. On a test battery sampling a wide variety of cognitive and motor abilities, significant intergroup differences occurred primarily on tasks with a primary motor component, although mild intergroup cognitive impairment was also demonstrated. The results suggested that maximal deterioration occurred during the first 5 years of symptoms, with few significant additional changes after that.

Motor performance after unilateral hemisphere damage in patients with tumor

Hemispheric asymmetry of sensory-motor control has been hypothesized on the basis of clinical and experimental data, but discrepant data indicate asymmetry may vary with task requirements. To examine this possibility, the performance of normal controls and patients with right or left hemispheric tumors were compared on a variety of motor tasks of varying complexity. Group differences were significant only for the two most complex of six tasks; since these two tasks differ in quality (proximal steadiness and distal dexterity), it is unlikely that quality differences are crucial. On these tasks, the group with left hemisphere damage demonstrated bilateral impairment while the right hemisphere group's deficits were contralateral to lesion site. These results support previous data and Liepmann's hypothesis of hemispheric asymmetry of sensory-motor control. Task complexity and the more specific hypothesis of sensory-motor sequencing are important factors influencing hemispheric asymmetry of control.