Neurophysiological indices of strategy development and skill acquisition

In order to examine neurophysiological changes associated with the development of cognitive and visuomotor strategies and skills, spectral features of the EEG were measured as participants learned to perform new tasks. In one experiment eight individuals practiced working memory tasks that required development of either spatial or verbal rehearsal and updating strategies. In a second experiment six individuals practiced a video game with a difficult visuomotor tracking component. The alpha rhythm, which is attenuated by functional cortical activation, was affected by task practice. In both experiments, a lower-frequency, centrally distributed alpha component increased between practice sessions in a task-independent fashion, reflecting an overall decrease in the extent of cortical activation after practice. A second, higher-frequency, posterior component of the alpha rhythm displayed task-specific practice effects. Practice in the verbal working memory task resulted in an increase of this signal over right posterior regions, an effect not seen after practice with the spatial working memory task or with the video game. This between-task difference presumably reflects a continued involvement of the posterior region of the right hemisphere in tasks that invoke visuospatial processes. This finding thus provides neurophysiological evidence for the formation of a task-specific neurocognitive strategy. In the second experiment a third component of the alpha rhythm, localized over somatomotor cortex, was enhanced in conjunction with acquisition of tracking skill. These alpha band results suggest that cortical regions not necessary for task performance become less active as skills develop. In both experiments the frontal midline (Fm) theta rhythm also displayed increases over the course of test sessions. This signal is associated with states of focused concentration, and its enhancement might reflect the conscious control over attention associated with maintenance of a task-appropriate mental set. Overall, the results suggest that the EEG can be used to monitor practice-related changes in the patterns of cortical activity that are associated with task processing. Additionally, these results highlight the importance of ensuring that subjects have developed stable strategies for performance before drawing inferences about the functional architecture underlying specific cognitive processes.     

Functional reorganization of the rat motor cortex following motor skill learning

Functional reorganization of the rat motor cortex following motor skill learning. J. Neurophysiol. 80: 3321-3325, 1998. Adult rats were allocated to either a skilled or unskilled reaching condition (SRC and URC, respectively). SRC animals were trained for 10 days on a skilled reaching task while URC animals were trained on a simple bar pressing task. After training, microelectrode stimulation was used to derive high resolution maps of the forelimb and hindlimb representations within the motor cortex. In comparison with URC animals, SRC animals exhibited a significant increase in mean area of the wrist and digit representations but a decrease in elbow/shoulder representation within the caudal forelimb area. No between-group differences in areal representation were found in either the hindlimb or rostral forelimb areas. These results demonstrate that motor skill learning is associated with a reorganization of movement representations within the rodent motor cortex.     

Mapping of semantic, phonological, and orthographic verbal working memory in normal adults with functional magnetic resonance imaging.

Twelve neurologically normal participants (4 men and 8 women) performed semantic, phonological, and orthographic working memory tasks and a control task during functional magnetic resonance imaging. Divergent regions of the posterior left hemisphere used for decoding and storage of information emerged in each working memory versus control task comparison. These regions were consistent with previous literature on processing mechanisms for semantic, phonological, and orthographic information. Further, working memory versus control task differences extended into the left frontal lobe, including premotor cortex, and even into subcortical structures. Findings were consistent with R. C. Martin and C. Romani's (1994) contention that different forms of verbal working memory exist and further suggest that a reconceptualization of premotor cortex functions is needed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional organization of the right nondominant cortex: Evidence from electrical stimulation.

Studied discrete functional localization for visuo-perceptual, spatial, and nonverbal memory tasks in conjunction with focal electrical stimulation of the exposed right-dominant cortex during awake craniotomies in 22 patients. Results provide evidence for discrete functional localization in the right, nondominant hemisphere. Performance on each task was significantly impaired in association with stimulation of some, but not all, sites in comparison with performance on nonstimulation control trials. There was, generally, a strong dissociation of sites involved in separate functions across individual Ss. Contrary to the notion of diffuse functional organization in the nondominant hemisphere, visuospatial functions in the right hemisphere appear to be as discretely localized as verbal functions in the left hemisphere. Language and language-related functions of naming, reading, short-term verbal memory, nonverbal oral-facial movement, and phonemic identification were assessed in a subgroup of 10 Ss in conjunction with right nondominant cortical stimulation. In right-handed Ss, no disruptions of these tasks were seen with stimulation of sites outside the right face motor cortex itself. In 2 case studies, there was evidence for right cortical involvement in the mediation of 2 nonphonetic symbol-based language systems: Japanese Kanji and Fortran. (French abstract) (72 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A hybrid computational model for ultrasound phased-array heating in presence of strongly scattering obstacles

BACKGROUND: Studies using electroencephalogram (EEG) measures of activation asymmetry have reported differences in anterior asymmetry between depressed and nondepressed subjects. Several studies have suggested reciprocal relations between measures of anterior and posterior activation asymmetries. We hypothesized that depressed subjects would fail to show the normal activation of posterior right hemisphere regions in response to an appropriate cognitive challenge. METHODS: EEG activity was recorded from 11 depressed and 19 nondepressed subjects during the performance of psychometrically matched verbal (word finding) and spatial (dot localization) tasks. Band power was extracted from all epochs of artifact-free data and averaged within each condition. Task performance was also assessed. RESULTS: Depressed subjects showed a specific deficit in the performance of the spatial task, whereas no group differences were evident on verbal performance. In posterior scalp regions, nondepressed controls had a pattern of relative left-sided activation during the verbal task and relative right-sided activation during the spatial task. In contrast, depressed subjects failed to show activation in posterior right hemisphere regions during spatial task performance. CONCLUSIONS: These findings suggest that deficits in right posterior functioning underlie the observed impairments in spatial functioning among depressed subjects.     

Cerebral blood flow relationships associated with a difficult tone recognition task in trained normal volunteers

Tone recognition is partially subserved by neural activity in the right frontal and primary auditory cortices. First we determined the brain areas associated with tone perception and recognition. This study then examined how regional cerebral blood flow (rCBF) in these and other brain regions correlates with the behavioral characteristics of a difficult tone recognition task. rCBF changes were assessed using H2(15)O positron emission tomography. Subtraction procedures were used to localize significant change regions and correlational analyses were applied to determine how response times (RT) predicted rCBF patterns. Twelve trained normal volunteers were studied in three conditions: REST, sensory motor control (SMC) and decision (DEC). The SMC-REST contrast revealed bilateral activation of primary auditory cortices, cerebellum and bilateral inferior frontal gyri. DEC-SMC produced significant clusters in the right middle and inferior frontal gyri, insula and claustrum; the anterior cingulate gyrus and supplementary motor area; the left insula/claustrum; and the left cerebellum. Correlational analyses, RT versus rCBF from DEC scans, showed a positive correlation in right inferior and middle frontal cortex; rCBF in bilateral auditory cortices and cerebellum exhibited significant negative correlations with RT These changes suggest that neural activity in the right frontal, superior temporal and cerebellar regions shifts back and forth in magnitude depending on whether tone recognition RT is relatively fast or slow, during a difficult, accurate assessment.     

Diaschisis in right putaminal hemorrhage: correlation with motor function

Local cerebral lesions may cause depression of function in remote areas of the brain presumably by a transneural mechanism; it has been called "diaschisis". In the present study, to investigate the relationship between motor function and "diaschisis" regional brain blood flow in hypertensive right putaminal hemorrhage was studied in 33 patients (mean age, 55 years; 22 men, 11 women). The hematoma was treated conservatively in 8 patients, aspirated stereotaxically in 9 patients, and evacuated through a craniotomy in 16 patients. The regional blood flow in the right motor cortex and the left cerebellar hemisphere was measured by a single photon emission CT with N-isopropyl-p- (123 I) iodo-amphetamine intravenous injection method, and was evaluated by the RI count on early image/the decay-corrected RI count on delayed image (E/D) value. The time during which regional brain blood flow was measured ranged from 29 to 35 days from the onset. There was a positive correlation between the grade in the motor function in the subacute stage and the regional blood flow in the right motor cortex and the left cerebellar hemisphere. There was also a positive correlation between the Barthel index in the chronic stage (mean follow-up periods: 40 months) and the regional blood flow in the right motor cortex and the left cerebellar hemisphere. The results of the present study suggest that in right putaminal hemorrhage the flow reduction in areas remote from the primary lesion, i.e., "diaschisis", may reflect not only the degree of functional abnormalities of the internal capsule, but also the possibility of functional recovery.     

Does the cerebellum contribute to cognitive aspects of speech production? A functional magnetic resonance imaging (fMRI) study in humans

Several positron emission tomography (PET) studies suggest a contribution of the lateral aspects of the right cerebellar hemisphere to higher-level (cognitive) aspects of speech production such as controlled verbal response selection. As an alternative, however, 'inner speech', giving rise to subliminal activity of orofacial and laryngeal muscles, might account for the observed activation effects. Eighteen subjects underwent functional magnetic resonance imaging (fMRI) during continuous silent recitation of the names of the months of the year ('automatic speech'). The right cerebellar hemisphere showed a significantly increased hemodynamic response concomitant with, among others, an asymmetric activation pattern towards the left side at the level of the motor strip. Since highly overlearned word strings, presumably, pose few demands on controlled response selection and since the projections of the right cerebellar hemisphere to the left precentral gyrus participate in motor control, the observed cerebellar activation, thus, seems to be related to the articulatory level of speech production rather than, as suggested by previous PET studies, to cognitive operations.     

Arthroscopy in food animal practice

1. Using positron emission tomography and measurement of regional cerebral blood flow (rCBF) as an index of cerebral activity we investigated the central processing of motor preparation in 13 healthy volunteers. 2. We used a motor reaction time paradigm with visual cues as preparatory and response signals. A preparatory stimulus (PS) provided either full, partial, or no information regarding two variables of a forthcoming right finger movement: finger type (index or little finger) and movement direction (abduction or elevation). After a variable delay period, a response stimulus (RS) prompted the movement. A condition was also tested in which the subject could freely select any of the four possible movements during the preparation period ("free" condition). The timing of events was designed to emphasize the motor preparation phase over the motor execution component during the scanning time of 1 min. 3. Distinct preparatory processes, which depended on the information contained in the PS, were demonstrated by significant differences in reaction time between conditions. The reaction time was shorter in the "full" and free conditions, intermediate in the two partial information conditions ("finger" and "direction"), and longer when no preparatory information was available ("none" condition). Conversely, movement time and movement amplitude were similar between conditions, establishing the constancy of the motor executive output. 4. In comparison with a "rest" condition, which had matched visual inputs, the different conditions of motor preparation were associated with increased rCBF in a common set of cerebral regions: the contralateral frontal cortex (sensorimotor, premotor, cingulate, and supplementary motor cortex), the contralateral parietal association cortex (anterior and posterior regions), the ipsilateral cerebellum, the contralateral basal ganglia, and the thalamus. This observation substantiates the participation of those cerebral structures in the preparation for movement. Furthermore, the similarity of the activated areas among the different conditions compared with the rest condition suggests a single anatomic substrate for motor preparation, independent of the movement information context. 5. Differing amounts of movement information contained in the PS affected rCBF changes in some cerebral regions. In particular, the rCBF in the anterior parietal cortex (Brodmann's area 40) was significantly larger in each of the full, finger, and direction conditions, individually, compared with the none condition. This observation supports the hypothesis that the anterior parietal association cortex plays a major role in the use of visual instructions contained in the PS for partial or complete preparation to perform a motor act. On the other hand, the posterior parietal association cortex (Brodmann's area 7) was more activated in the finger, direction, and none conditions than in the full condition. This increased activity with restricted advance information suggests that the posterior region of the parietal cortex is concerned with correct movement selection on the basis of enhanced spatial attention to the RS. 6. In contrast with the parietal cortex, the secondary motor areas (i.e, premotor cortex, cingulate cortex, and supplementary motor area) showed similar activity regardless of the degree of preparation allowed by the advance visual information. Thus the parietal cortex may play a more crucial role than the secondary motor areas in integrating visual information in preparation for movement. 7. The effect on brain activity of the internal (self-generated) versus the external (cued) mode of movement selection was assessed by comparing the free and full conditions, the preparatory component being matched in the two conditions. The anterior part of the supplementary motor area was the main area preferentially involved in the internal selection of movement, independently of motor preparation processes.     

Relationship of specific EEG frequencies at specific brain areas with performance

This study shows that incorrect responses are preceded by different EEG characteristics than correct responses, and that these differences appear in specific brain regions that participate in each particular task. EEGs were recorded in children during three different tasks: color discrimination (CDT), verbal working memory (VWM), and word categorization task (WCT). EEG segments previous to the presentation of the stimulus were analysed. Incorrect responses were preceded by lower EEG power values at 7.8 Hz in posterior temporal and right parietal leads in CDT, 8.59 and 9.36 Hz in frontal areas in VWM, and 10.72 Hz in the left hemisphere in WCT. In the former task > 1.56 Hz power in frontal areas prior to an incorrect response was also observed.     

Asymmetrical effects of unilateral cortical suction lesions: Behavioral characterization.

Assessed behavioral effects of unilateral frontocortical suction lesions in the right and left hemispheres in 24 male Sprague-Dawley rats, using a computerized activity monitoring system. Lesions of the right frontal cortex produced postoperative hyperactivity consisting of increases in the total distance traveled, average distance per movement, and average speed of movement. Vertical, rotational, and stereotypic measures were not changed. Ss receiving left hemisphere lesions did not differ from sham-operated controls on any behavioral variable. The lateralized hyperactivity resulting from lesions of the right frontal cortex was confined to increased length and speed of horizontal movement and did not appear to represent a generalized increase in all components of spontaneous activity. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motor responses measured by brain electrical activity mapping.

Studied the brain electrical activity of 14 right-handed normal Ss (mean age 25 yrs) while they were exposed to motor performance tasks of increasing difficulty. Each task lasted 45–60 sec, and a 30-sec period of each task was analyzed by a spectrum analyzer. Data are presented in topographic maps showing the electrical activity for each task, in different frequency bands. Results show a bilateral decrease in amplitude in sensorimotor areas relative to baseline for a single hand movement. Tasks that required the programming of movement showed baseline–task differences in amplitude in additional areas: the right frontal area, the prefrontal area, the posterior parietal area, and the left temporal area. Findings suggest that different topographical areas are involved in motor tasks that require an increased level of programming. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Does the cerebellum contribute to mental skills?

Proposes a new concept of cerebellar capabilities that is based both on neural evidence and on information processing theory. It is suggested that the phylogenetically newest structures of the cerebellum may contribute to mental skills in much the same way that the phylogenetically older structures contribute to motor skills. In both cases, the cerebellum can send signals from the dentate nucleus to the cerebral frontal cortex via the thalamus. Signals from the older part of the dentate nucleus help the frontal motor cortex to effect the skilled manipulation of muscles, and signals from the newest part of the dentate nucleus may help the frontal association cortex to effect the skilled manipulation of information or ideas. It is shown how such mental skills could have evolved in higher primates in the course of phylogenetic and ontogenetic development. The validity of this new concept of cerebellar function can be tested on humans by means of tomographic brain scans. (133 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Handedness and asymmetry of hand representation in human motor cortex

The cortical representation of five simple hand and finger movements in the human motor cortex was determined in left- and right-handed people with whole-head magnetoencephalography. Different movements were found to be represented by spatially segregated dipolar sources in primary motor cortex. The spatial arrangement of neuronal sources for digit and wrist movements was nonsomatotopic and varied greatly between subjects. As an estimator of hand area size in primary motor cortex, we determined the smallest cuboid volume enclosing the five dipole sources within the left and right hemisphere of each subject. Interhemispheric comparison revealed a significant increase of this volume in primary motor cortex opposite to the preferred hand. This asymmetry was due to a greater spatial segregation of neuronal dipole generators subserving different hand and finger actions in the dominant hemisphere. Mean Euclidean distances between dipole sources for different movements were 10.7 +/- 3.5 mm in the dominant and 9.4 +/- 3.5 mm in the nondominant hemisphere (mean +/- SD; P = 0. 01, two-tailed t-test). The expansion of hand representation in primary motor cortex could not simply be attributed to a greater number of pyramidal cells devoted to each particular movement as inferred from current source amplitudes. The degree of hemispheric asymmetry of hand area size in the primary motor cortex was correlated highly with the asymmetry of hand performance in a standardized handedness test (r = -0.76, P < 0.01). These results demonstrate for the first time a biological correlate of handedness in human motor cortex. The expansion of hand motor cortex in the dominant hemisphere may provide extra space for the cortical encoding of a greater motor skill repertoire of the preferred hand.     

Cortical networks implicated in semantic and episodic memory: common or unique?

While previous functional neuroimaging studies have shown that semantic and episodic memory tasks activate different cortical regions, they never compared regional cerebral blood flow (rCBF) patterns associated with semantic and episodic memory within the same experimental design. In this study, we used H2(15)O PET to study subjects in the course of semantic and episodic memory tasks. rCBF was measured in 9 normal volunteers during a resting baseline condition and two cognitive tasks. In the semantic categorisation task subjects heard a list of concrete words and had to respond to words belonging to the "animals" or "food" category. In the episodic recognition task subjects heard a list of concrete words, half "old", i.e. belonging to the list of the semantic categorisation task, and half "new", i.e. presented for the first time. Subjects had to respond to the "old" words. Both tasks were compared to a resting condition. Statistical analysis was performed with Statistical Parametric Mapping (SPM). Compared to the resting condition, the semantic tasks, activated the superior temporal gyri bilaterally, the left frontal cortex, and right premotor cortex. The episodic tasks activated the left superior temporal gyrus, the frontal cortex bilaterally, and the right inferior parietal cortex. Compared to the episodic memory tasks, the semantic memory tasks activated the superior temporal/insular cortex bilaterally and the right premotor cortex. Compared to the semantic memory tasks, the episodic memory tasks activated the right frontal cortex. These results suggest that cortical networks implicated in semantic and episodic memory show both common and unique regions, with the right prefrontal cortex being the neural correlate specific of episodic remembering.     

A test-retest study of cerebral blood flow during somatosensory stimulation in depressed patients with schizophrenia and major depression

Six depressed patients with schizophrenia and 6 depressed patients with major depression were investigated before and during somatosensory stimulation (SS) with Tc-99m HMPAO SPECT. 8 controls were investigated only under resting conditions. The results can be summarized as follows: 1. Both psychiatric patient groups were hypofrontal (dorsolateral prefrontal cortex) compared to controls. 2. Hypofrontality was further enhanced by SS, significantly only in affective psychoses in the right inferior frontal lobe and in the right frontal hemisphere in total, in schizophrenia in the left dorsolateral prefrontal cortex. 3. Within the frontal lobes different regions were affected by SS in the two diagnostic groups. 4. In the right inferior parietal lobe SS response was significantly different in the two illnesses with schizophrenia showing a relative decrease, affective psychoses showing a relative increase of activity. 5. SS produced an increase of cerebral blood flow in subcortical regions (statistically significant contralateral to SS in thalamus and basal ganglia, ipsilateral to SS in cerebellum), a pattern which was common to all psychiatric patients. 6. Somatosensory cortex flow was not changed by SS. In conclusion, we could not fully confirm our hypotheses that similar blood flow abnormalities in different illnesses during SS are only caused by similarities in depressive psychopathology. Instead, depressed patients with schizophrenia were different from depressed patients with major depression in showing decreased activity in interrelating brain regions participating in an attentional network.     

Control of maximum sarcoplasmic reticulum Ca load in intact ferret ventricular myocytes. Effects Of thapsigargin and isoproterenol

Functional neuroanatomical correlates subserving maintenance rehearsal relative to a reading control task were investigated with positron emission tomography imaging of cerebral blood flow in 6 healthy older participants and 6 patients with mild Alzheimer's disease (AD). Rehearsal and reading rates and number of unique words rehearsed did not differ significantly for the 2 groups. The right dorsolateral prefrontal cortex was activated in both groups during rehearsal, highlighting this region's role in short-term maintenance of verbal information. A shift in cortical processing resources to more anterior brain regions with increased rehearsal list length was seen, likely reflecting greater demands on frontal cortex as cognitive load grows. Whereas controls showed unilateral right frontal activation during rehearsal, AD patients demonstrated bilateral frontal activation, possibly reflecting compensatory recruitment of neural resources.     

Visualization of the information flow through human oculomotor cortical regions by transcranial magnetic stimulation

We investigated the topography of human cortical activation during an antisaccade task by focal transcranial magnetic stimulation (TMS). We used a figure-eight shaped coil, with the stimulus intensity set just above the threshold for activation of the hand motor areas but weak enough not to elicit blinks. TMS was delivered at various time intervals (80, 100, and 120 ms) after target presentation over various sites on the scalp while the subjects performed the antisaccade task. It was possible to elicit a mild but significant delay in saccade onset over 1) the frontal regions (a region 2-4 cm anterior and 2-4 cm lateral to hand motor area) and 2) posterior parietal regions (6-8 cm posterior and 0-4 cm lateral to hand motor area) regardless of which hemisphere was stimulated. The frontal regions were assumed to correspond to a cortical region including the frontal eye fields (FEFs), whereas the parietal regions were assumed to represent a wide region that includes the posterior parietal cortices (PPCs). The regions inducing the delay shifted from the posterior parietal regions at an earlier interval (80 ms) to the frontal regions at a later interval (100 ms), which suggested an information flow from posterior to anterior cortical regions during the presaccadic period. At 120 ms, the effect of TMS over the frontal regions still persisted but was greatly diminished. Erroneous prosaccades to the presented target were elicited over a wide cortical region including the frontal and posterior parietal regions, which again showed a forward shift with time. However, the distribution of effective regions exhibited a clear contralateral predominance in terms of saccade direction. Our technique provides a useful method not only for detecting the topography of cortical regions active during saccadic eye movement, but also for constructing a physiological map to visualize the temporal evolution of functional activities in the relevant cortical regions.     

Prefrontal Brain Magnetic Activity: Effects of Memory Task Demands.

Changes in spatiotemporal profiles of brain magnetic activity were investigated in healthy volunteers as a function of varying demands for phonological storage of spoken pseudowords. Greater activity for the phonological memory task was restricted to the dorsolateral prefrontal cortex (DLPFC) in the left hemisphere. During performance of the memory task, activity was initially found in the left superior temporal gyrus (between 100 and 200 ms), followed by activity in the ventrolateral prefrontal, motor, and premotor cortices (between 200 and 300 ms). Activity in DLPFCs was first observed consistently across participants later, between 300 and 400 ms. The data are consistent with the purported role of posterior temporal cortices in phonological analysis and in the online storage of phonological information, the contribution of ventrolateral and motor processing areas in establishment and short-term maintenance of articulatory representations through rehearsal, and the role of DLPFCs in the executive control of the maintenance operation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Numerical bifurcation analysis of distance-dependent on-center off-surround shunting neural networks

Cortical functions concerned with the execution of skilled movements can be studied through complex interactive tasks. Skilled performance task (SPT) offers the greatest deal of information about the electrophysiological components reflecting pre-programming, execution of the movement and control of the results. Overall, these components are indicated as "movement-related brain macropotentials' (MRBMs). Among them, Bereitschaftspotential (BP) reflects cerebral processes related to the preparation of movement and skilled performance positivity (SPP) reflects control processes on the result of performance. There is some evidence supporting a training effect on MRBMs, but less clear is whether long-term practice of a skilled activity could modify learning strategies of a new skilled task. We recorded MRBMs in subjects trained for a long time to perform a highly skillful athletic activity, i.e. gun shooting, and in a group of control subjects without any former experience in skilled motor activities. Our findings demonstrated the existence of a relationship between pre-programming and performance control, as suggested by decrease of BP amplitude and increase of SPP amplitude in presence of high levels of performance. Long-term practice seems to develop better control models on performance, that reduce the need of a high mental effort in pre-programming a skilled action.