Tomasz Wolak

The effect of motivation on working memory: An fMRI and SEM study

This study investigated the effective connectivity between prefrontal regions of human brain supporting motivational influence on working memory. Functional magnetic resonance imaging (fMRI) and structural equation modeling (SEM) were used to examine the interaction between the lateral orbitofrontal (OFC), medial OFC, and dorsolateral prefrontal (DLPFC) regions in the left and right hemisphere during performance of the verbal 2-back working memory task under two reinforcement conditions. The low-motivation condition was not associated with monetary reinforcement, while the high-motivation condition involved the probability of winning a certain amount of money. In the low-motivation condition, the OFC regions in both hemispheres positively influenced the left DLPFC activity. In the high-motivation condition, the connectivity in the network including the right OFC regions and left DLPFC changed from positive to negative, whereas the positive connectivity in the network composed of the left OFC and left DLPFC became slightly enhanced compared with the low-motivation condition. However, only the connection between the right lateral OFC and left DLPFC showed a significant condition-dependent change in the strength of influence conveyed through the pathway. This change appears to be the functional correlate of motivational influence on verbal working memory.

Changes in fMRI BOLD response to increasing and decreasing task difficulty during auditory perception of temporal order.

We have discovered changes in brain activation during difficult and easy milliseconds timing. Structures engaged in difficult and easier auditory temporal-order judgment were identified in 17 young healthy listeners presented with paired-white-noises of different durations. Within each pair, a short (10 ms) and a long (50 ms) noise was separated by a silent gap of 10, 60 or 160 ms, corresponding to three levels of task difficulty, i.e. difficult, moderate and easy conditions, respectively. A block design paradigm was applied. In temporal-order judgment task subjects were required to define the order of noises within each pair, i.e. short-long or long-short. In the control task they only detected the presentation of the stimulus pair. A multiple regression with task difficulty as a regressor (difficult, moderate, easy) showed dynamic changes in neural activity. Increasing activations accompanying increased task difficulty were found in both bilateral inferior parietal lobuli and inferior frontal gyri, thus, in classic regions related to attentional and working memory processes. Conversely, decreased task difficulty was accompanied by increasing involvement of more specific timing areas, namely bilateral medial frontal gyri and left cerebellum. These findings strongly suggest engagement of different neural networks in difficult or easier timing and indicate a framework for understanding timing representation in the brain.

Functional imaging with MR T1 contrast: a feasibility study with blood-pool contrast agent.

The aim of this study was to prove the concept of using a long intravenous half-life blood-pool T1 contrast agent as a new functional imaging method. For each of ten healthy subjects, two dynamic magnetic resonance (MR) protocols were carried out: (1) a reference run with a typical T2* echo-planar imaging (EPI) sequence based on the blood oxygenation level-dependent (BOLD) effect and (2) a run with a T1-sensitive three-dimensional (3D) gradient-echo (GRE) sequence using cerebral blood volume (CBV) contrast after intravenous administration of a contrast agent containing a chelate of gadolinium diethylene-triamine-pentaacetate with a phosphono-oxymethyl substituent. All sequences were performed during the execution of a block-type finger-tapping paradigm. SPM5 software was used for statistical analysis. For both runs maximum activations (peak Z-scoreu2009=u20095.5, cluster size 3,449 voxels) were localized in the left postcentral gyrus. Visual inspection of respective signal amplitudes suggests the T1 contrast to be substantially smaller than EPI (0.5% vs 1%). A new functional imaging method with potentially smaller image artefacts due to the nature of CBV contrast and characteristics of the T1 sequence was proposed and verified.

Coronary blood flow measurement from x-ray images: experiment performed on the artery model

The paper presents the experimental validation of the coronary blood flow measured from coronarographic images. The method of flow measurement earlier presented is based on elements of the indicator-dilution theory and on the idea of using two sequences of images obtained during standard coronarographic examination. Measurements of the image intensity along the cross-section lines of the artery were performed on the sequence with the standard injection of contrast and with the small quantity of slowly injected contrast. These two sequences enable the construction of the contrast relative concentration curve in the defined earlier cross-section vs. time. The global volumetric blood flow can be calculated as a ratio of the quantity of the indicator injected during the indicator-dilution sequence by the value of the area under concentration curve. Experimental validation was performed using a simple artery model. Results of the flow calculation for five cross-section lines positioned in different intensity levels regions of the image show that the error is below 20%.

A blood pool contrast aided T1 functional MRI in patients with brain tumors—a preliminary study

IntroductionThe aim of our study was to determine the possibility of using a new functional technique: a T1-dependent sequence with administration of blood pool contrast agent (BPCA), in patients with brain tumors before and after surgical treatment. We also aimed to compare our results with those obtained using the fMRI technique, based on Blood Oxygenation Level-Dependent (BOLD) contrast.MethodsFor each of our 14 oncologic patients (four before and ten after neurosurgical intervention), we obtained: a T1-3D GRE sequence (TRu2009=u20092.6xa0ms/TEu2009=u20091.1xa0ms/FAu2009=u200910°) after intravenous administration of BPCA (0.03xa0mmol/kg), as well as a T2*EPI sequence (TRu2009=u20093xa0s/TEu2009=u200950xa0ms/FAu2009=u200990°). Movement and/or tactile block type paradigms were carried out during both functional runs. SPM5 software was used for analysis.ResultsFor both functional techniques, maximum activations were localized in the same areas. There were no significant differences observed in the t values calculated for activations located in the primary motor cortex between groups of pre- and post-intervention patients (in the same functional technique). The mean values for T2* EPI examinations were 10.84 and 9.36, respectively. The mean t values for the T1 technique were lower, especially for the post-intervention patients (5.83 and 3.9, respectively).ConclusionsThe T1 technique can be used to detect functional areas in patients with brain tumors, pre-, and post-surgical intervention. This technique enables the evaluation of cortical centers that suffer from susceptibility artifacts when using the T2* BOLD technique. Activations found using both techniques have the same localization, with lower values for the T1 technique.

Wykorzystanie jednoczesnych rejestracji słuchowych potencjałów korowych i funkcjonalnego rezonansu magnetycznego do badania procesów ośrodkowej części układu słuchowego – wyniki wstępneApplication of simultaneous auditory evoked potentials and functional magnetic resonance recordings for examination of central auditory system – preliminary results☆☆☆☆☆☆

INTRODUCTIONnProcessing of auditory information in central nervous system bases on the series of quickly occurring neural processes that cannot be separately monitored using only the fMRI registration. Simultaneous recording of the auditory evoked potentials, characterized by good temporal resolution, and the functional magnetic resonance imaging with excellent spatial resolution allows studying higher auditory functions with precision both in time and space.nnnTHE AIM OF THE STUDYnwas to implement the simultaneous AEP-fMRI recordings method for the investigation of information processing at different levels of central auditory system.nnnMATERIAL AND METHODSnFive healthy volunteers, aged 22-35 years, participated in the experiment. The study was performed using high-field (3T) MR scanner from Siemens and 64-channel electrophysiological system Neuroscan from Compumedics. Auditory evoked potentials generated by acoustic stimuli (standard and deviant tones) were registered using modified odd-ball procedure. Functional magnetic resonance recordings were performed using sparse acquisition paradigm. The results of electrophysiological registrations have been worked out by determining voltage distributions of AEP on skull and modeling their bioelectrical intracerebral generators (dipoles). FMRI activations were determined on the basis of deviant to standard and standard to deviant functional contrasts. Results obtained from electrophysiological studies have been integrated with functional outcomes.nnnRESULTSnMorphology, amplitude, latency and voltage distribution of auditory evoked potentials (P1, N1, P2) to standard stimuli presented during simultaneous AEP-fMRI registrations were very similar to the responses obtained outside scanner room. Significant fMRI activations to standard stimuli were found mainly in the auditory cortex. Activations in these regions corresponded with N1 wave dipoles modeled based on auditory potentials generated by standard tones. Auditory evoked potentials to deviant stimuli were recorded only outside the MRI scanner. However, deviant stimuli induced significant fMRI activations. They were observed mainly in the anterior cingulate gyrus, insula and parietal lobes. These regions of the brain are related to attention and decision-making processes.nnnCONCLUSIONSnThe results showed that applied paradigm is suitable for investigation of acoustic processing on the level of auditory cortex. Technique of the simultaneous AEP-fMRI registrations seems to be promising for investigation of more complex nervous processes in central auditory system with good temporo-spatial resolution.Summary Introduction Processing of auditory information in central nervous system bases on the series of quickly occurring neural processes that cannot be separately monitored using only the fMRI registration. Simultaneous recording of the auditory evoked potentials, characterized by good temporal resolution, and the functional magnetic resonance imaging with excellent spatial resolution allows studying higher auditory functions with precision both in time and space. The aim of the study was to implement the simultaneous AEP-fMRI recordings method for the investigation of information processing at different levels of central auditory system. Material and methods Five healthy volunteers, aged 22–35 years, participated in the experiment. The study was performed using high-field (3T) MR scanner from Siemens and 64-channel electrophysiological system Neuroscan from Compumedics. Auditory evoked potentials generated by acoustic stimuli (standard and deviant tones) were registered using modified odd-ball procedure. Functional magnetic resonance recordings were performed using sparse acquisition paradigm. The results of electrophysiological registrations have been worked out by determining voltage distributions of AEP on skull and modeling their bioelectrical intracerebral generators (dipoles). FMRI activations were determined on the basis of deviant to standard and standard to deviant functional contrasts. Results obtained from electrophysiological studies have been integrated with functional outcomes. Results Morphology, amplitude, latency and voltage distribution of auditory evoked potentials (P1, N1, P2) to standard stimuli presented during simultaneous AEP-fMRI registrations were very similar to the responses obtained outside scanner room. Significant fMRI activations to standard stimuli were found mainly in the auditory cortex. Activations in these regions corresponded with N1 wave dipoles modeled based on auditory potentials generated by standard tones. Auditory evoked potentials to deviant stimuli were recorded only outside the MRI scanner. However, deviant stimuli induced significant fMRI activations. They were observed mainly in the anterior cingulate gyrus, insula and parietal lobes. These regions of the brain are related to attention and decision-making processes. Conclusions The results showed that applied paradigm is suitable for investigation of acoustic processing on the level of auditory cortex. Technique of the simultaneous AEP-fMRI registrations seems to be promising for investigation of more complex nervous processes in central auditory system with good temporo-spatial resolution.

Wykorzystanie jednoczesnych rejestracji słuchowych potencjałów korowych i funkcjonalnego rezonansu magnetycznego do badania procesów ośrodkowej części układu słuchowego – wyniki wstępne ☆ ☆☆ ☆☆☆

INTRODUCTIONnProcessing of auditory information in central nervous system bases on the series of quickly occurring neural processes that cannot be separately monitored using only the fMRI registration. Simultaneous recording of the auditory evoked potentials, characterized by good temporal resolution, and the functional magnetic resonance imaging with excellent spatial resolution allows studying higher auditory functions with precision both in time and space.nnnTHE AIM OF THE STUDYnwas to implement the simultaneous AEP-fMRI recordings method for the investigation of information processing at different levels of central auditory system.nnnMATERIAL AND METHODSnFive healthy volunteers, aged 22-35 years, participated in the experiment. The study was performed using high-field (3T) MR scanner from Siemens and 64-channel electrophysiological system Neuroscan from Compumedics. Auditory evoked potentials generated by acoustic stimuli (standard and deviant tones) were registered using modified odd-ball procedure. Functional magnetic resonance recordings were performed using sparse acquisition paradigm. The results of electrophysiological registrations have been worked out by determining voltage distributions of AEP on skull and modeling their bioelectrical intracerebral generators (dipoles). FMRI activations were determined on the basis of deviant to standard and standard to deviant functional contrasts. Results obtained from electrophysiological studies have been integrated with functional outcomes.nnnRESULTSnMorphology, amplitude, latency and voltage distribution of auditory evoked potentials (P1, N1, P2) to standard stimuli presented during simultaneous AEP-fMRI registrations were very similar to the responses obtained outside scanner room. Significant fMRI activations to standard stimuli were found mainly in the auditory cortex. Activations in these regions corresponded with N1 wave dipoles modeled based on auditory potentials generated by standard tones. Auditory evoked potentials to deviant stimuli were recorded only outside the MRI scanner. However, deviant stimuli induced significant fMRI activations. They were observed mainly in the anterior cingulate gyrus, insula and parietal lobes. These regions of the brain are related to attention and decision-making processes.nnnCONCLUSIONSnThe results showed that applied paradigm is suitable for investigation of acoustic processing on the level of auditory cortex. Technique of the simultaneous AEP-fMRI registrations seems to be promising for investigation of more complex nervous processes in central auditory system with good temporo-spatial resolution.Summary Introduction Processing of auditory information in central nervous system bases on the series of quickly occurring neural processes that cannot be separately monitored using only the fMRI registration. Simultaneous recording of the auditory evoked potentials, characterized by good temporal resolution, and the functional magnetic resonance imaging with excellent spatial resolution allows studying higher auditory functions with precision both in time and space. The aim of the study was to implement the simultaneous AEP-fMRI recordings method for the investigation of information processing at different levels of central auditory system. Material and methods Five healthy volunteers, aged 22–35 years, participated in the experiment. The study was performed using high-field (3T) MR scanner from Siemens and 64-channel electrophysiological system Neuroscan from Compumedics. Auditory evoked potentials generated by acoustic stimuli (standard and deviant tones) were registered using modified odd-ball procedure. Functional magnetic resonance recordings were performed using sparse acquisition paradigm. The results of electrophysiological registrations have been worked out by determining voltage distributions of AEP on skull and modeling their bioelectrical intracerebral generators (dipoles). FMRI activations were determined on the basis of deviant to standard and standard to deviant functional contrasts. Results obtained from electrophysiological studies have been integrated with functional outcomes. Results Morphology, amplitude, latency and voltage distribution of auditory evoked potentials (P1, N1, P2) to standard stimuli presented during simultaneous AEP-fMRI registrations were very similar to the responses obtained outside scanner room. Significant fMRI activations to standard stimuli were found mainly in the auditory cortex. Activations in these regions corresponded with N1 wave dipoles modeled based on auditory potentials generated by standard tones. Auditory evoked potentials to deviant stimuli were recorded only outside the MRI scanner. However, deviant stimuli induced significant fMRI activations. They were observed mainly in the anterior cingulate gyrus, insula and parietal lobes. These regions of the brain are related to attention and decision-making processes. Conclusions The results showed that applied paradigm is suitable for investigation of acoustic processing on the level of auditory cortex. Technique of the simultaneous AEP-fMRI registrations seems to be promising for investigation of more complex nervous processes in central auditory system with good temporo-spatial resolution.

Dynamic T1 functional MRI examinations with use of blood pool contrast agent--an approach to optimization of the technique.

The goal was to optimize dynamic T1 imaging for functional MRI (fMRI) examinations. For each of the 10 healthy subjects T1 3D gradient echo sequence (GRE) sequences were provided immediately after administration of blood pool contrast agent then every 2 h when subjects performed block finger tapings. Dynamic T1 fMRI is sensitive to detect cortical activations up to 6 h after BPCA administration. fMRI should be conducted within 2 h of CA administration, which is enough time for a typical fMRI experiment procedure.

Optimal plane search method in blood flow measurements by magnetic resonance imaging

This paper offers an algorithm for determining the blood flow parameters in the neck vessel segments using a single (optimal) measurement plane instead of the usual approach involving four planes orthogonal to the artery axis. This new approach aims at significantly shortening the time required to complete measurements using Nuclear Magnetic Resonance techniques. Based on a defined error function, the algorithm scans the solution space to find the minimum of the error function, and thus to determine a single plane characterized by a minimum measurement error, which allows for an accurate measurement of blood flow in the four carotid arteries. The paper also comprises a practical implementation of this method (as a module of a larger imaging-measuring system), including preliminary research results.