Cortical Activation in Mental Rotation and the Role of the Corpus Callosum: Observations in Healthy Subjects and Split-Brain Patients

none6The mental rotation (MR) is an abstract mental operation thanks to which a person imagines rotating an object or a body part to place it in an other position. The ability to perform MR was belived to belong to the right hemisphere for objects, and to the left for one’s ownbody images. Mental rotation is considered to be basic for imitation with the anatomical perspective, which in turn is needed for social interactions and learning. Altered imitative performances have been reported in patients with resections or microstructure alterations of the corpus callosum (CC). These patients also display a reduced MR ability compared to control subjects, as shown in a recent behavioral study. The difference was statistically significant, leading us to hypothesize a role of the CC to integrate the two hemispheres’ asymmetric functions. The present study was designed to detect, by means of a functional MRI, the cortical activation evoked during an MR task in healthy control subjects and callosotomized patients. The results suggest that performing MR requires activation of opercular cortex and inferior parietal lobule in either hemispheres, and likely the integrity of the CC, thus confirming that the main brain commissure is involved in cognitive functions.openPierpaoli, Chiara; Ghoushi, Mojgan; Foschi, Nicoletta; Lattanzi, Simona; Fabri, Mara; Polonara, GabrielePierpaoli, Chiara; Ghoushi, Mojgan; Foschi, Nicoletta; Lattanzi, Simona; Fabri, Mara; Polonara, Gabriel

Relationship between Burr-Hole position and pneumocephalus in patients operated for chronic subdural hematoma

Objective: Chronic subdural hematoma (CSDH) is one of the most frequent neurosurgical conditions in people aging between 70 and 80 years. The cranial burr-hole (CBH) with surgical cavity irrigation through the burr hole and closed drainage system is the treatment of choice but -post-operative outcome can be influenced by pneumocephalus. In this study, we aimed to explore the relationship between the anterior-posterior (AP) burr-hole position and the volume of post-operative pneumocephalus. Patients and Methods: We identified 153 consecutive patients who underwent BHC for CSDH at our institution. Baseline and post-operative data were retrospectively collected from medical records. The linear regression model was used to estimate the association between the volume of post-operative subdural air collection and burr-hole position along with other baseline patients and hematoma variables. Results: The AP position of the burr-hole was independently associated with the volume of post-operative pneumocephalus: lower volume of subdural air was observed in patients with more anterior cranial burr-hole. Conclusions: In patients operated for CSDH, the cranial burr-hole should be performed anteriorly to grant a lesser amount of subdural post-operative air collection

SELECTIVE ASSOCIATIVE PHONAGNOSIA AFTER RIGHT ANTERIOR TEMPORAL STROKE

We report the case of a 48 year old men who developed a selective impairment in famous voice recognition after ischemic stroke in right subcortical structures (lenticular nucleus and head of the caudate) and right anterior temporal lobe. He underwent fibrinolytic treatment. During the following days he progressively recovered and was discharged without neurological focal sign. Patent foramen ovale was found. When he got back to his house he noticed that he was unable to recognize the voice of his favoured singers and needed to ask who was the singer to his relatives. Neuropsychological examination revealed a selective impairment in famous voice recognition in the absence of alteration of voice perception, face perception and famous face recognition. All other neuropsychological domains were spared. In particular language, memory and executive functions were intact. Neuroimaging carried out by means of PET and MRI revealed two small ischemic lesions in the right subcortical region, involving lenticular and caudate nuclei and in the right temporal pole. To our knowledge, this is the first case described in literature of a patient showing a selective associative phonagnosia after right anterior temporal stroke. The present case helps to clarify the brain circuits underlying famous voice recognition and adds evidence in favour of a right hemisphere involvement in processing knowledge of familiar voices. These findings are discussed in relation to current models of brain organization of person-specific and general semantic knowledge.

Visual integration across fixation: automatic processes are split but conscious processes remain unified in the split-brain

The classic view holds that when “split-brain” patients are presented with an object in the right visual field, they will correctly identify it verbally and with the right hand. However, when the object is presented in the left visual field, the patient verbally states that he saw nothing but nevertheless identifies it accurately with the left hand. This interaction suggests that perception, recognition and responding are separated in the two isolated hemispheres. However, there is now accumulating evidence that this interaction is not absolute; for instance, split-brain patients are able to detect and localise stimuli anywhere in the visual field verbally and with either hand. In this study we set out to explore this cross-hemifield interaction in more detail with the split-brain patient DDC and carried out two experiments. The aim of these experiments is to unveil the unity of deliberate and automatic processing in the context of visual integration across hemispheres. Experiment 1 suggests that automatic processing is split in this context. In contrast, when the patient is forced to adopt a conscious, deliberate, approach, processing seemed to be unified across visual fields (and thus across hemispheres). First, we looked at the confidence that DDC has in his responses. The experiment involved a simultaneous “same” versus “different” matching task with two shapes presented either within one hemifield or across fixation. The results showed that we replicated the observation that split brain patients cannot match across fixation, but more interesting, that DDC was very confident in the across-fixation condition while performing at chance-level. On the basis of this result, we hypothesised a two-route explanation. In healthy subjects, the visual information from the two hemifields is integrated in an automatic, unconscious fashion via the intact splenium, and this route has been severed in DDC. However, we know from previous experiments that some transfer of information remains possible. We proposed that this second route (perhaps less visual; more symbolic) may become apparent when he is forced to use a deliberate, consciously controlled approach. In an experiment where he is informed, by a second stimulus presented in one hemifield, what to do with the first stimulus that was presented in the same or the opposite hemifield, we showed that there was indeed interhemispheric transfer of information. We suggest that this two-route model may help in clarifying some of the controversial issues in split-brain research

More accurate macro-models of solid oxide fuel cells through electrochemical and microstructural parameter estimation - Part II: Parameter estimation

This paper presents a systematic synergetic approach between experimental measurements, equivalent circuit modelling (described in Part I) and macro-scale modelling theory which has proved to be instrumental for the estimation of microstructural and electrochemical features of a Ni- YSZ|YSZ|Pr2NiO4+δ-GDC solid oxide fuel cell (SOFC). The aforementioned parameters have been used to generate a more accurate CFD macro-model which has been validated against the experimental results (presented in Part III)

Functional topography of the corpus callosum as revealed by fMRI and behavioural studies of control subjects and patients with callosal resection

The concept of a topographical map of the corpus callosum (CC), the main interhemispheric commissure, has emerged from human lesion studies and from anatomical tracing investigations in other mammals. Over the last few years, a rising number of researchers have been reporting functional magnetic resonance imaging (fMRI) activation in also the CC. This short review summarizes the functional and behavioral studies performed in groups of healthy subjects and in patients undergone to partial or total callosal resection, and it is focused on the work conducted by the authors. Functional data have been collected by diffusion tensor imaging and tractography (DTI and DTT) and functional magnetic resonance imaging (fMRI), both techniques allowing to expand and refine our knowledge of the commissure. Neuropsychological test were also administered, and simple behavioral task, as imitation perspective and mental rotation ability, were analyzed. These researches added new insight on the topographic organization of the human CC. By combining DTT and fMRI it was possible to observe that the callosal crossing points of interhemispheric fibers connecting homologous primary sensory cortices, correspond to the CC sites where the fMRI activation elicited by peripheral stimulation was detected. In addition, CC activation during imitation and mental rotation performance was also reported. These studies demonstrated the presence of specific callosal fiber tracts that cross the commissure in the genu, body, and splenium, at sites showing fMRI activation, consistently with cortical activated areas. Altogether, these findings lend further support to the notion that the CC displays a functional topographic organization, also related to specific behavior

Turbo-FLAIR sequence in brain MRI

To compare a turbo-FLAIR sequence with Proton Density (PD) and T2- weighted Turbo Spin-Echo (TSE) sequences in several different brain diseases, 276 MRI examinations were performed on a 1.0 Tesla system. The positive cases were assessed for lesion detection and lesion conspicuity. Four quantitative criteria were also used to compare the contrast of the two techniques: lesion to background contrast, lesion to background contrast to noise ratio (CNR), lesion to Cerobrospinal fluid (CSF) contrast, lesion to CSF contrast to noise ratio. The turbo FLAIR sequence was found to be superior to PD and T2- weighted TSE for lesion detection: this sequence detected more lesions in 74 patients than PD and in 42 patients than T2, but missed some subtentorial lesions. For lesion conspicuity turbo-FLAIR was judged equivalent to PD and T2-weighted TSE respectively in 27% and 45% of the cases and better in 71% and 53% of the cases. Lesion to background contrast and lesion to background CNR were found to be significantly greater for turbo-FLAIR than for PD (p<0.001). Compared with T2-weighted TSE, turbo-FLAIR showed a significantly higher lesion to background contrast (p<0.001) and inferior lesion to background CNR (p<0.001). Our study indicates that turbo-FLAIR can replace PD TSE scans in most cases and can be used as a first choice sequence for cerebrovascular diseases, multiple sclerosis and for the evaluation of gliosis

FUNCTIONAL TOPOGRAPHY OF HUMAN CORPUS CALLOSUM: AN fMRI MAPPING STUDY

The concept of a topographical map of the corpus callosum (CC) has emerged from human lesion studies and from electrophysiological and anatomical tracing investigations in other mammals. Over the last few years a rising number of researchers have been reporting functional magnetic resonance imaging (fMRI) activation in white matter, particularly the CC. In this study the scope for describing CC topography with fMRI was explored by evoking activation through simple sensory stimulation and motor tasks. We reviewed our published and unpublished fMRI and diffusion tensor imaging data on the cortical representation of tactile, gustatory, auditory, and visual sensitivity and of motor activation, obtained in 36 normal volunteers and in 6 patients with partial callosotomy. Activation foci were consistently detected in discrete CC regions: anterior (taste stimuli), central (motor tasks), central and posterior (tactile stimuli), and splenium (auditory and visual stimuli). Reconstruction of callosal fibers connecting activated primary gustatory, motor, somatosensory, auditory, and visual cortices by diffusion tensor tracking showed bundles crossing, respectively, through the genu, anterior and posterior body, and splenium, at sites harboring fMRI foci. These data confirm that the CC commissure has a topographical organization and demonstrate that its functional topography can be explored with fMRI