N.J. Shah

Cortical activations in primary and secondary motor areas for complex bimanual movements in professional pianists

Hemodynamic responses were measured applying functional magnetic resonance imaging in two professional piano players and two carefully matched non-musician control subjects during the performance of self-paced bimanual and unimanual tapping tasks. The bimanual tasks were chosen because they resemble typical movements pianists have to generate during piano exercises. The results showed that the primary and secondary motor areas (M1, SMA, pre-SMA, and CMA) were considerably activated to a much lesser degree in professional pianists than in non-musicians. This difference was strongest for the pre-SMA and CMA, where professional pianists showed very little activation. The results suggest that the long lasting extensive hand skill training of the pianists leads to greater efficiency which is reflected in a smaller number of active neurons needed to perform given finger movements. This in turn enlarges the possible control capacity for a wide range of movements because more movements, or more degrees of freedom, are controllable.

Cortical activations during paced finger-tapping applying visual and auditory pacing stimuli.

In order to study neural systems which are involved in motor timing we used whole-brain functional resonance imaging while subjects performed a paced finger-tapping task (PFT) with their right index finger. During one condition, subjects were imaged while tapping in synchrony with tones separated by a constant interval (auditory synchronisation, AS), followed by tapping without the pacing stimulus (auditory continuation, AC). In another condition, subjects were imaged while tapping in synchrony with a visual stimulus presented at the same frequency as the tones (visual synchronisation, VS) followed by a tapping sequence without visual pacing (visual continuation, VC). The following main results were obtained: (1) tapping in the context of visual pacing was generally more variable than tapping in the context of auditory stimuli; (2) during all conditions, a fronto-parietal network was active including the dorsal lateral premotor cortex (dPMC), M1, S1, inferior parietal lobule (LPi), supplementary motor cortex (SMA), the right cerebellar hemisphere, and the paravermial region; (3) stronger activation in the bilateral ventral premotor cortex (vPMC), the left LPi, the SMA, the right inferior cerebellum, and the left thalamus during both auditory conditions (AS and AC) compared to the visual conditions (VS and VC); (4) stronger activation in the right superior cerebellum, the vermis, and the right LPi during the visual conditions (VS and VC); (5) similar activations for the AS and AC conditions; but (6) marked differences between the VS and VC conditions especially in the dorsal premotor cortex (dPMC) and LPi areas; and (7) finally, there were no activations in the auditory and visual cortices when the pacing stimuli were absent. These findings were taken as evidence for a general difference between the motor control modes operative during the auditory and visual conditions. Paced finger tapping in the context of auditory pacing stimuli relies more on brain structures subserving internal motor control while paced finger-tapping in the context of visual pacing stimuli relies on brain structures relying on the subserving processing or imagination of visual pacing stimuli.

Intensity coding of auditory stimuli: an fMRI study

The effect of stimulus intensity (sound pressure level, SPL) of auditory stimuli on the BOLD response in the auditory cortex was investigated in 14 young and healthy subjects, with no hearing abnormalities, using echo-planar, functional magnetic resonance imaging (fMRI) during a verbal and a non-verbal auditory discrimination task. The stimuli were presented block-wise at three different intensities: 95, 85 and 75 dB (SPL). All subjects showed fMRI signal increases in superior temporal gyrus (STG) covering primary and secondary auditory cortex. Most importantly, the spatial extent of the fMRI response in STG increased with increasing stimulus intensity. It is hypothesized that spreading of excitation is associated with the encoding of increasing stimulus intensity levels. In addition, we found bifrontal activation supposedly evoked by the auditory-articulary loop of working memory. The results presented here should assist in the design of optimal activation strategies for studying the auditory cortex with fMRI paradigms and may help in understanding intensity coding of auditory stimuli.

Does dichotic listening probe temporal lobe functions

ObjectiveTo explore cortical hemodynamic responses using fMRI in the context of three dichotic listening tasks. BackgroundDichotic listening is a widely used behavioral technique indicating brain laterality during which subjects are presented with two different auditory signals at the same time, one arriving at each ear. fMRI offers the potential to explore the hemodynamic response during dichotic listening and to relate the behavioral indices with these cortical measures. MethodfMRI was performed for 10 right-handed normal subjects listening to consonant–vowel syllable pairs with the task of detecting a “target” syllable by pressing a button. The target stimulus appeared equally often in the left and right ear. The subjects were instructed to either concentrate on the stimuli presented in both ears (DIV) or only in the left ear (FL) or right ear (FR). In addition, a control condition was used during which the syllables were presented binaurally. Hemodynamic responses were measured by applying whole-head echo planar imaging techniques and statistically analyzed by using statistical parametric mapping (SPM99) software. ResultsDuring dichotic listening, there were generally extended activations in frontotemporal networks. For the DIV condition, the authors found strong bilateral activations in the inferior frontal gyrus, Broca’s area, the left middle frontal gyrus, and in the left superior temporal gyrus. During the FL condition, there was an additional cluster in the right inferior frontal gyrus. For the FR condition, there were stronger activations in Broca’s area and the left superior temporal gyrus. ConclusionsThese findings were taken as evidence that dichotic listening is more demanding, requiring more processing capacity distributed in frontotemporal networks. The behavioral measures of dichotic listening were not simply a function of temporal lobe activation. Rather, the cortical activations support the notion that different processing strategies controlled by different neural structures are applied during dichotic listening.

Tapping movements according to regular and irregular visual timing signals investigated with fMRI.

Whole-head functional MR images were acquired while 10 subjects were asked to tap with their right index finger in synchrony with a visual stimulus appearing regularly with a frequency of 1.5 Hz, or irregularly with a mean frequency of 1.5 Hz. Performance data show that during regular tapping most taps were close to stimulus onset. However, when the subjects paced their tapping according to the irregular stimuli, most taps appeared about 300 ms after the onset of the pacing stimuli. Comparing the brain activations resulting from regular tapping with those from irregular tapping, we found increased activation in left precuneus only. Comparing irregular versus regular tapping shows increased activity in right cerebellar nuclei and vermis, left ventrolateral thalamus, left sensorimotor cortex, left and right pre-SMA and left SMA proper. These results show that during irregular pacing the motor areas are more strongly activated than during regular pacing. In addition, further neural systems are involved in the motor control during irregular pacing: cerebellar vermis and a cerebellothalamo-cortical system. The latter is supposedly involved in error correction in the context of visually guided movements.

A new method for fast quantitative mapping of absolute water content in vivo.

The presence of brain edema, in its various forms, is an accompanying feature of many diseased states. Although the localized occurrence of brain edema may be demonstrated with MRI, the quantitative determination of absolute water content, an aspect that could play an important role in the objective evaluation of the dynamics of brain edema and the monitoring of the efficiency of treatment, is much more demanding. We present a method for the localized and quantitative measurement of absolute water content based on the combination of two fast multi-slice and multi-time point sequences QUTE and TAPIR for mapping the T(2)* and T(1) relaxation times, respectively. Incorporation of corrections for local B(1) field miscalibrations, temperature differences between the subject and a reference probe placed in the FOV, receiver profile inhomogeneities and T(1) saturation effects are included and allow the determination of water content with anatomical resolution and a precision >98%. The method was validated in phantom studies and was applied to the localized in vivo measurement of water content in a group of normal individuals and a patient with brain tumor. The results demonstrate that in vivo measurement of regional absolute water content is possible in clinically relevant measurement times with a statistical and systematic measurement error of <2%.

Top-down and bottom-up modulation of language related areas - An fMRI Study

BackgroundOne major problem for cognitive neuroscience is to describe the interaction between stimulus and task driven neural modulation. We used fMRI to investigate this interaction in the human brain. Ten male subjects performed a passive listening and a semantic categorization task in a factorial design. In both tasks, words were presented auditorily at three different rates.ResultsWe found: (i) as word presentation rate increased hemodynamic responses increased bilaterally in the superior temporal gyrus including Heschls gyrus (HG), the planum temporale (PT), and the planum polare (PP); (ii) compared to passive listening, semantic categorization produced increased bilateral activations in the ventral inferior frontal gyrus (IFG) and middle frontal gyrus (MFG); (iii) hemodynamic responses in the left dorsal IFG increased linearly with increasing word presentation rate only during the semantic categorization task; (iv) in the semantic task hemodynamic responses decreased bilaterally in the insula with increasing word presentation rates; and (v) in parts of the HG the hemodynamic response increased with increasing word presentation rates during passive listening more strongly.ConclusionThe observed rate effect in primary and secondary auditory cortex is in accord with previous findings and suggests that these areas are driven by low-level stimulus attributes. The bilateral effect of semantic categorization is also in accord with previous studies and emphasizes the role of these areas in semantic operations. The interaction between semantic categorization and word presentation in the left IFG indicates that this area has linguistic functions not present in the right IFG. Finally, we speculate that the interaction between semantic categorization and word presentation rates in HG and the insula might reflect an inhibition of the transfer of unnecessary information from the temporal to frontal regions of the brain.

Topographic segregation and convergence of verbal, object, shape and spatial working memory in humans

This functional magnetic resonance imaging study investigates commonalties and differences in working memory (WM) processes employing different types of stimuli. We specifically sought to characterize topographic convergence and segregation with respect to prefrontal cortex involvement using verbal, spatial, real object and shape memory items in a two-back WM task. Both the dorsolateral and ventrolateral prefrontal cortices are conjointly activated across all stimulus types. No stimulus-specific differences in the activation patterns of the prefrontal cortex could be demonstrated giving support to the view of an amodal prefrontal involvement during WM processes. However, extra-frontal regions specialized on feature processing and involved in the preprocessing of the stimuli were selectively activated by these different subtypes of WM. These selectively activated regions are assigned to parts of the ventral and dorsal stream.

A New Method for Fast Multislice T1 Mapping

Abstract A sequence for T 1 relaxation-time mapping which enables high-resolution, multislice imaging in short acquisition times is presented. The sequence is based on the Look-Locker method and employs a magnetization-preparation module prior to data acquisition with a banded k -space data collection scheme. The method was implemented on a standard clinical scanner and the accuracy of the T 1 results was evaluated against spectroscopic measurements. The accuracy of the T 1 maps validated by phantom imaging measurements is T 1 ≅ 2000 ms) and is around 1% for faster-relaxing species ( T 1 ≤ 1200 ms). Additionally, the inherent multislice, multipoint capability of the method is demonstrated. Multislice, multipoint in vivo results of the human brain obtained using this method are presented. An acquisition time of approximately 8 min was achieved for a T 1 map, which, in principle, can provide whole-brain coverage with 25 slices, a matrix size of 256 × 256, and 12 time points. The speed of the sequence is derived through optimized interleaving of slices and time points, together with the acquisition of multiple echoes, which are used to fill a 3-segment k -space.

Fast T1 mapping with volume coverage

Four different sequences which enable high‐resolution, multislice T1 relaxation‐time mapping are presented. All these sequences are based on the Look‐Locker method with differences arising from the use of either a saturation‐recovery or inversion‐recovery module prior to data acquisition with a full k‐space or banded k‐space acquisition scheme. The methods were implemented on a standard clinical scanner and the accuracy of the T1 results was evaluated against spectroscopic measurements. The accuracy of the T1 maps validated by phantom imaging measurements is around 1% for species which relax with T1 times that mimic gray/white matter (T1 ≤ 1000 ms). Additionally, the inherent multislice, multipoint capability of the methods is demonstrated. Finally, in vivo results of the human brain obtained using the faster method are presented. The fastest data acquisition was achieved with a saturation‐recovery, banded k‐space method where k‐space was divided into three segments; an overall acquisition time of around 5 min (for species with T1 ≤ 1 sec) was achieved for a T1 map which can, in principle, provide whole‐brain coverage with a matrix size of 256 × 256 at multiple time‐points. Magn Reson Med 46:131–140, 2001.