The cortical motor system of primates is formed by a mosaic of anatomically and functionally distinct areas. These areas are not only involved in motor functions, but also play a role in functions formerly attributed to higher order associative cortical areas. In the present review, we discuss three types of higher functions carried out by the motor cortical areas: sensory-motor transformations, action understanding, and decision processing regarding action execution. We submit that generating internal representations of actions is central to cortical motor function. External contingencies and motivational factors determine then whether these action representations are transformed into actual actions. (+info)
Parahippocampal reactivation signal at retrieval after interruption of rehearsal.
(2/17)
Verbal information is maintained on-line within working memory by rehearsal. However, we still can recall the verbal information when rehearsal is interrupted. Here we show that this is achieved by reactivation of maintained information. We used event-related functional magnetic resonance imaging to identify brain activation at encoding, during memory delay, and at retrieval, within the same trial of a verbal working memory task. On half of the trials, retrieval was tested after arithmetic distraction to interrupt rehearsal of the remembered verbal items. We found that the parahippocampal cortex (PHC) was highly active at retrieval on trials with distraction compared with trials without distraction. The PHC did not show sustained activation during the memory delay. By contrast, the dorsolateral prefrontal cortex (DLPF), left superior temporal region (ST), and Broca's area showed sustained activation during the memory delay, suggesting their role in maintenance of verbal items. After arithmetic distraction, the DLPF and ST were engaged in arithmetic processing. Thus, these areas could not maintain the verbal items during the distraction. At retrieval of verbal items after the distraction, the DLPF, ST and Broca's area were also active. The activity was taken to reflect reactivated representation of the verbal items. The primary role of the PHC in retrieval may be to trigger the reactivation of these cortical areas that had maintained the remembered items, thereby reactivating the information that is no longer maintained on-line. (+info)
Dissociation between conflict detection and error monitoring in the human anterior cingulate cortex.
(3/17)
The relative importance of the anterior cingulate cortex (ACC) for the detection and resolution of response conflicts versus its role in error monitoring remains under debate. One disputed issue is whether conflict detection and error monitoring can be viewed as unitary functions performed by the same region of the ACC, or whether these processes can be dissociated functionally and anatomically. We used a combination of electrophysiological and neuropsychological methods to assess these competing hypotheses. A neurological patient with a rare focal lesion of rostral-to-middorsal ACC was tested in an event-related potential study designed to track the time course of neural activity during conflicts and erroneous responses. Compared with controls, the error-related negativity component after incorrect responses was attenuated in the patient, accompanied by lower error-correction rates. Conversely, the stimulus-locked component on correct conflict trials, the N450, was enhanced, and behavioral performance was impaired. We hypothesize that intact regions of lateral prefrontal cortex were able to detect response conflict, but damage to the dorsal ACC impaired response inhibition, which may be due to disconnection from cingulate and supplementary motor areas. The results implicate rostral-dorsal ACC in error monitoring and suggest this function can be dissociated from conflict-detection processes. (+info)
A new classification of higher level gait disorders in patients with cerebral multi-infarct states.
(4/17)
BACKGROUND: cerebral multi-infarct states may lead to gait disorders in the absence of cognitive impairment. Where these gait disorders occur in the absence of neurological signs they have been termed gait apraxia or more recently higher-level gait disorders. In this paper we hypothesise three main types based on presumptive sites of anatomical damage: (a) Ignition Apraxia, where damage is predominantly in the supplementary motor area and its connections, with good responses to external clues; (b) Equilibrium Apraxia, where damage is predominantly in the pre-motor area in its connections, with poor responses to external cues and (c) Mixed Gait Apraxia. SUBJECTS: the clinical features and measured gait parameters of 13 patients with cerebral multi-infarct states and higher-level gait disorder are described (7 with Ignition Apraxia and 6 with Equilibrium Apraxia) along with those of 6 healthy elderly control subjects. METHODS: baseline gait characteristics were assessed on a walkway, which measured the following: step lengths, width of base and velocity. RESULTS: measured baseline gait parameters support the above hypothesis. CONCLUSIONS: it is suggested, though not proven, that patients with Ignition Apraxia could have problems with internal cueing due to lesions in the supplementary motor area or its connections whereas those with Equilibrium Apraxia could have dysfunction predominantly in the pre-motor area and its connections. (+info)
Functional dissociation among components of remembering: control, perceived oldness, and content.
(5/17)
Remembering is the ability to bring back to mind episodes from one's past and is presumably accomplished by multiple, interdependent processes. In the present functional magnetic resonance imaging study, neural correlates of three hypothesized components of remembering were explored, including those associated with control, perceived oldness, and retrieved content. Levels of each component were separately manipulated by varying study procedures and sorting trials by subject response. Results suggest that specific regions in the left prefrontal cortex, including anterior-ventral Brodmann's Area (BA) 45/47 and more dorsal BA 44, increase activity when high levels of control are required but do not necessarily modulate on the basis of perceived oldness. Parietal and frontal regions, particularly the left parietal cortex near BA 40/39, associate with the perception that information is old and generalize across levels of control and retrieved content. Activity in the parietal cortex correlated with perceived oldness even when judgments were in error. The inferior temporal cortex near BA 19/37 associated differentially with retrieval of visual object content. Within the ventral visual processing stream, content-based modulation was specific to late object-responsive regions, suggesting an efficient retrieval process that spares areas that process more primitive retinotopically mapped visual features. Taken collectively, the results identify neural correlates of distinct components of remembering and provide evidence for a functional dissociation. Frontal regions may contribute to control processes that interact with different posterior regions that contribute a signal that information is old and support the contents of retrieval. (+info)
Neurocognitive functioning in AD/HD, predominantly inattentive and combined subtypes.
(6/17)
The Predominantly Inattentive (PI) and Combined (CB) subtypes of AD/HD differ in cognitive tempo, age of onset, gender ratio, and comorbidity, yet a differentiating endophenotype has not been identified. The aim of this study was to test rigorously diagnosed PI, CB, and typical children on measures selected for their potential to reveal hypothesized differences between the subtypes in specific neurocognitive systems (anterior vs. posterior attentional systems) and processes (arousal vs. activation). Thirty-four CB and 26 PI children meeting full DSM-IV criteria for subtype both in school and at home, without confounding reading disability or emotional disorder, were enrolled along with 20 typically developing children. Neurocognitive functions measured included attention, inhibitory control, working memory, learning, and executive functions. Tasks included the Stroop, Wisconsin Card Sorting Test, Continuous Performance Test (CPT). Buschke Selective Reminding Test, ad the Tower of London (TOL), as well as instruments developed by Posner and Sternberg, and tasks assessing the impact on reaction time of [corrected] varying preparatory intervals and stimulus/response complexity. After co-varying for IQ, subtypes differed primarily on measures of impulsivity during tests of vigilance (CPT) and executive function (TOL), with the CB group showing greater impulsivity than both other groups. In addition, the PI group showed worse performance than CB and control groups on the WISC-III Processing Speed Index. Whether analyzed with or without an IQ co-variate, there was no support in the data for hypothesized differences between subtypes in functioning of the anterior vs. posterior attentional systems, nor in involvement of arousal vs. activation processes. The results indicate that the PI and CB subtypes are best differentiated by ratings, observations and tests of cognitive tempo and behavioral impulsivity. Neuropsychological methods have yet to identify critical neuropsychological [corrected] substrates of these differences. (+info)
The role of the cerebellum in schizophrenia.
(7/17)