1,721,070 research outputs found
Misprojection of landmarks onto the spatial map
No full textIt has been suggested that neglect patients misrepresent the metric spatial relations along the horizontal axis (anisometry). The "fabric" of their internal spatial medium would be distorted in such a way that physically equal distances appear relatively shorter on the contralesional side (canonical anisometry). The case of GL, a 76-year-old lady with left neglect on visual search tasks, is presented. GL showed severe relative overestimation on the left (contralesional) side on two independent tasks evaluating the metrics of her internal representation. A qualitatively similar pattern was found in two out of 10 other neglect patients who performed the second task. This behavior cannot be accounted for by the canonical anisometry hypothesis. Nevertheless, GL produced a relative left overextension (underestimation) when trying to set the endpoints of a virtual line given its midpoint (Endpoints Task). An interpretation of these results is offered in terms of a misprojection of relevant landmarks onto the internal representation without assuming distortion of its "fabric.
Basi fisiologiche dell’attività psichica
No full textCapitolo riguardante gli elementi fondamentali delle Neuroscienze per studenti universitari
Learning hierarchically structured action sequences is unaffected by prefrontal-cortex lesion
No full textThis study tested the impact of prefrontal-cortex lesion on learning hierarchically structured action sequences. Using a visual-manual serial reaction time task, we had subjects first perform five blocks of trials with a hierarchically structured 14-element action sequence and then tested for sequence-specific learning by introducing a pseudo-random transfer sequence. Relative to control subjects (N = 39), we found that both lateral frontal (N = 16) and medial frontal (N = 18) patients showed reduced overall performance benefits across the training phase. In contrast, the negative transfer test showed significantly increased reaction times in all patient groups, indicating robust sequence-specific learning. This learning was not significantly different from that of the control group. Taken together, the data suggest that learning hierarchically structured action sequences is unimpaired in patients with prefrontal-cortex lesion
Neural representations of hierarchical rule sets: The human control system represents rules irrespective of the hierarchical level to which they belong
No full textHumans use rules to organize their actions to achieve specific goals. Although simple rules that link a sensory stimulus to one response may suffice in some situations, often, the application of multiple, hierarchically organized rules is required. Recent theories suggest that progressively higher level rules are encoded along an anterior-to-posterior gradient within PFC. Although some evidence supports the existence of such a functional gradient, other studies argue for a lesser degree of specialization within PFC. We used fMRI to investigate whether rules at different hierarchical levels are represented at distinct locations in the brain or encoded by a single system. Thirty-seven male and female participants represented and applied hierarchical rule sets containing one lower-level stimulus-response rule and one higher-level selection rule. We used multivariate pattern analysis to investigate directly the representation of rules at each hierarchical level in absence of information about rules from other levels or other task-related information, thus providing a clear identification of low- and high-level rule representations. We could decode low- and high-level rules from local patterns of brain activity within a wide frontoparietal network. However, no significant difference existed between regions encoding representations of rules from both levels except for precentral gyrus, which represented only low-level rule information. Our findings show that the brain represents conditional rules regardless of their level in the explored hierarchy, so the human control system did not organize task representation according to this dimension. Our paradigm represents a promising approach to identifying critical principles that shape this control system
Right atrial hemangioma
No full textA case of right atrial hemangioma as a rare tumor of the heart is reported. Because of its single, pedunculated mass, surgical excision of the tumor resulted in the complete treatment. Histologically, it was classified as arteriolar type. The importance of recent non-invasive techniques to diagnose these tumors during life is emphasized
Semantic fluency: cognitive basis and diagnostic performance in focal dementias and Alzheimer's Disease.
No full textBetter without (lateral) frontal cortex? Insight problems solved by frontal patients
No full textA recently proposed theory on frontal lobe functions claims that the prefrontal cortex, particularly its dorso-lateral aspect, is crucial in defining a set of responses suitable for a particular task, and biasing these for selection. This activity is carried out for virtually any kind of non-routine tasks, without distinction of content. The aim of this study is to test the prediction of Frith's 'sculpting the response space' hypothesis by means of an 'insight' problem-solving task, namely the matchstick arithmetic task. Starting from Knoblich et al.'s interpretation for the failure of healthy controls to solve the matchstick problem, and Frith's theory on the role of dorsolateral frontal cortex, we derived the counterintuitive prediction that patients with focal damage to the lateral frontal cortex should perform better than a group of healthy participants on this rather difficult task. We administered the matchstick task to 35 patients (aged 26-65 years) with a single focal brain lesion as determined by a CT or an MRI scan, and to 23 healthy participants (aged 34-62 years). The findings seemed in line with theoretical predictions. While only 43% of healthy participants could solve the most difficult matchstick problems ('type C'), 82% of lateral frontal patients did so (Fisher's exact test, P < 0.05). In conclusion, the combination of Frith's and Knoblich et al.'s theories was corroborated
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