fMRI and acoustic analyses reveal neural correlates of gestural complexity and articulatory effort within bilateral inferior frontal gyrus during speech production

In an event-related fMRI study of overt speech production, we investigated the relationship between gestural complexity and underlying brain activity within bilateral inferior frontal gyrus (IFG). We operationalized gestural complexity as the number of active articulatory tiers (glottal, oral, nasal) and the degree of fine-grained temporal coordination between tiers (low, high). Forty-three neurotypical participants produced three types of highly-frequent non-word CV-syllable sequences, which differ systematically in gestural complexity (simple: ['dadada], intermediate: ['tatata], complex: ['nanana]). Comparing blood oxygen level-dependent (BOLD) responses across complexity conditions revealed that syllables with greater gestural complexity elicited increased activation patterns. Moreover, when durational parameters were included as covariates in the analyses, significant effects of articulatory effort were found over and above the effects of complexity. The results suggest that these differences in BOLD-response reflect the differential contribution of articulatory mechanisms that are required to produce phonologically distinct speech sounds.

Is it still speech? Different processing strategies in learning to discriminate stimuli in the transition from speech to non-speech including feedback evaluation

Processing of speech was investigated by using stimuli gradually changing from speech (vowels) to non-speech (spectral rotated vowels). Stimuli were presented in descending levels of vocalization blends, from pure speech to non-speech, through step-wise combinations, resulting in ambiguous versions of the sounds. Participants performed a two-alternative forced choice task: categorization of sounds were made according to whether they contained more speech or non-speech. Performance feedback was presented visually on each trial. Reaction times (RT) after sound presentation, and functional magnetic resonance imaging (fMRI) data during auditory and visual processing, were analyzed. RT data suggested individual differences with a distinct group, good performers, functioning better in distinguishing stimuli with a higher degree of ambiguous blends compared to poor performers, who were not able to distinguish these stimuli correctly. fMRI data confirmed this finding. During auditory stimulation, good performers showed neural activation in the ventral auditory pathway, including the primary auditory cortex and the anterior superior temporal sulcus (responsible for speech processing). Poor performers, in contrast, showed neural activation in the dorsal auditory pathway, including the bilateral superior temporal gyrus. Group differences were also found for visual feedback processing. Differences observed between the groups were interpreted as reflecting different neural processing strategies.

Heidelberg Neuro-Music Therapy Restores Attention-Related Activity in the Angular Gyrus in Chronic Tinnitus Patients

Background: Tinnitus is the perception of a phantom sound without external acoustic stimulation. Recent tinnitus research suggests a relationship between attention processes and tinnitus-related distress. It has been found that too much focus on tinnitus comes at the expense of the visual domain. The angular gyrus (AG) seems to play a crucial role in switching attention to the most salient stimulus. This study aims to evaluate the involvement of the AG during visual attention tasks in tinnitus sufferers treated with Heidelberg Neuro-Music Therapy (HNMT), an intervention that has been shown to reduce tinnitus-related distress. Methods: Thirty-three patients with chronic tinnitus, 45 patients with recent-onset tinnitus, and 35 healthy controls were tested. A fraction of these (21/21/22) were treated with the "compact" version of the HNMT lasting 1 week with intense treatments, while non-treated participants were included as passive controls. Visual attention was evaluated during functional Magnet-Resonance Imaging (fMRI) by a visual Continous Performance Task (CPT) using letter-based alarm cues ("O" and "X") appearing in a sequence of neutral letters, "A" through "H." Participants were instructed to respond via button press only if the letter "O" was followed by the letter "X" (GO condition), but not to respond if a neutral letter appeared instead (NOGO condition). All participants underwent two fMRI sessions, before and after a 1-week study period. Results: The CPT results revealed a relationship between error rates and tinnitus duration at baseline whereby the occurrence of erroneous "GO omissions" and the reaction time increased with tinnitus duration. Patients with chronic tinnitus who were treated with HNMT had decreasing error rates (fewer GO omissions) compared to treated recent-onset patients. fMRI analyses confirmed greater activation of the AG during CPT in chronic patients after HNMT treatment compared to treated recent-onset patients. Conclusions: Our findings suggest that HNMT treatment helps shift the attention from the auditory phantom percept toward visual cues in chronic tinnitus patients and that this shift in attention may involve the AG.

Heidelberg Neuro-Music Therapy Enhances Task-Negative Activity in Tinnitus Patients

Background: Suffering from tinnitus causes mental distress in most patients. Recent findings point toward a diminished activity of the brain's default-mode network (DMN) in subjects with mental disorders including depression or anxiety and also recently in subjects with tinnitus-related distress. We recently developed a therapeutic intervention, namely the Heidelberg Neuro-Music Therapy (HNMT), which shows an effective reduction of tinnitus-related distress following a 1-week short-term treatment. This approach offers the possibility to evaluate the neural changes associated with the improvements in tinnitus distress. We previously reported gray matter (GM) reorganization in DMN regions and in primary auditory areas following HNMT in cases of recent-onset tinnitus. Here we evaluate on the same patient group, using functional MRI (fMRI), the activity of the DMN following the improvements tinnitus-related distress related to the HNMT intervention.

Methods: The DMN activity was estimated by the task-negative activation (TNA) during long inter-trial intervals in a word recognition task. The level of TNA was evaluated twice, before and after the 1-week study period, in 18 treated tinnitus patients (“treatment group,” TG), 21 passive tinnitus controls (PTC), and 22 active healthy controls (AC). During the study, the participants in TG and AC groups were treated with HNMT, whereas PTC patients did not receive any tinnitus-specific treatment. Therapy-related effects on DMN activity were assessed by comparing the pairs of fMRI records from the TG and PTC groups.

Results: Treatment of the TG group with HNMT resulted in an augmented DMN activity in the PCC by 2.5% whereas no change was found in AC and PTC groups. This enhancement of PCC activity correlated with a reduction in tinnitus distress (Spearman Rho: −0.5; p < 0.005).

Conclusion: Our findings show that an increased DMN activity, especially in the PCC, underlies the improvements in tinnitus-related distress triggered by HNMT and identify the DMN as an important network involved in therapeutic improvements.

[fMRI and DTI in delayed development of number processing]

The neuronal correlate of the current cultural performance arose from developmental processes that can be observed by functional and anatomical magnetic resonance imaging. The velocity of these maturation processes occurs differently between adolescents, causing implications for both school career and academic performance. Regarding spatial-numerical cognition the myelinization of the superior longitudinal bundle appears to be crucial because this fiber connection intermediates between the linguistic nature of number words and conception of their spatial-numerical magnitude. The neuroscientific observation of anatomical brain maturation and its influence on school-relevant number processing may be helpful for educational purposes as well as for school psychology.

Cortical reorganization in recent-onset tinnitus patients by the Heidelberg Model of Music Therapy

Pathophysiology and treatment of tinnitus still are fields of intensive research. The neuroscientifically motivated Heidelberg Model of Music Therapy, previously developed by the German Center for Music Therapy Research, Heidelberg, Germany, was applied to explore its effects on individual distress and on brain structures. This therapy is a compact and fast application of nine consecutive 50-min sessions of individualized therapy implemented over 1 week. Clinical improvement and long-term effects over several years have previously been published. However, the underlying neural basis of the therapy's success has not yet been explored. In the current study, the therapy was applied to acute tinnitus patients (TG) and healthy active controls (AC). Non-treated patients were also included as passive controls (PTC). As predicted, the therapeutic intervention led to a significant decrease of tinnitus-related distress in TG compared to PTC. Before and after the study week, high-resolution MRT scans were obtained for each subject. Assessment by repeated measures design for several groups (Two-Way ANOVA) revealed structural gray matter (GM) increase in TG compared to PTC, comprising clusters in precuneus, medial superior frontal areas, and in the auditory cortex. This pattern was further applied as mask for general GM changes as induced by the therapy week. The therapy-like procedure in AC also elicited similar GM increases in precuneus and frontal regions. Comparison between structural effects in TG vs. AC was calculated within the mask for general GM changes to obtain specific effects in tinnitus patients, yielding GM increase in right Heschl's gyrus, right Rolandic operculum, and medial superior frontal regions. In line with recent findings on the crucial role of the auditory cortex in maintaining tinnitus-related distress, a causative relation between the therapy-related GM alterations in auditory areas and the long-lasting therapy effects can be assumed.

Selective transfer of visual working memory training on Chinese character learning

Previous research has shown a systematic relationship between phonological working memory capacity and second language proficiency for alphabetic languages. However, little is known about the impact of working memory processes on second language learning in a non-alphabetic language such as Mandarin Chinese. Due to the greater complexity of the Chinese writing system we expect that visual working memory rather than phonological working memory exerts a unique influence on learning Chinese characters. This issue was explored in the present experiment by comparing visual working memory training with an active (auditory working memory training) control condition and a passive, no training control condition. Training induced modulations in language-related brain networks were additionally examined using functional magnetic resonance imaging in a pretest-training-posttest design. As revealed by pre- to posttest comparisons and analyses of individual differences in working memory training gains, visual working memory training led to positive transfer effects on visual Chinese vocabulary learning compared to both control conditions. In addition, we found sustained activation after visual working memory training in the (predominantly visual) left infero-temporal cortex that was associated with behavioral transfer. In the control conditions, activation either increased (active control condition) or decreased (passive control condition) without reliable behavioral transfer effects. This suggests that visual working memory training leads to more efficient processing and more refined responses in brain regions involved in visual processing. Furthermore, visual working memory training boosted additional activation in the precuneus, presumably reflecting mental image generation of the learned characters. We, therefore, suggest that the conjoint activity of the mid-fusiform gyrus and the precuneus after visual working memory training reflects an interaction of working memory and imagery processes with complex visual stimuli that fosters the coherent synthesis of a percept from a complex visual input in service of enhanced Chinese character learning.

[Functional MRI of speech]

Speech is a multifactorial term. In relationship with our central organ, speech is a communication medium which in a complex manner includes the production and perception of verbal information. Even within this limitation, imaging exploration of the neuronal basis of verbal communication offers an extensive investigative field which can only be presented in this article as highlights. The main focus is on the technical hurdles of investigations into speech production using functional magnetic resonance imaging (fMRI) and solution options will be presented. The difficulties contained in this aspect are that spoken words can only be poorly assessed in the noise level of the measurements and that the movements of the mouth necessary for speech motoric can lead to technical imaging artefacts. Investigation techniques and designs will be discussed which allow a representation of speech-relevant brain centers despite these problems.

fMRI correlates of working memory: specific posterior representation sites for motion and position information

We assume that working memory is provided by a network comprising domain-general anterior and different domain-specific posterior brain areas depending on the type of stimulus and the task demands. Based on imaging studies from perception, we hypothesized that dynamic spatial (motion) and static spatial (position) information can be dissociated during retention in working memory. Participants were presented with a moving dot. About one second after stimulus presentation, a cue indicated whether its motion or end position should be held in memory. Six seconds later, a second stimulus was shown which was to be compared with the first one with respect to identity on the cued dimension. In the baseline condition, the cue indicated that no memory task would follow. We contrasted activity during maintenance of the different features. Differential activations in regions related to motion perception (area hMT/V5+, superior temporal sulcus) were observed in the motion working memory task. For position working memory, enhanced activations in a right brain region at the temporo-parieto-occipital junction emerged. The results are discussed with respect to domain-specific regions active in perception and how they can be also involved in short term retention for those very features. It is suggested that two types of spatial information categories can be dissociated: dynamic spatial (motion) and static spatial (position) information seem to be processed by different working memory structures.

Hyperechogenicity of the substantia nigra in healthy controls is related to MRI changes and to neuronal loss as determined by F-Dopa PET

Transcranial ultrasound (TCS) has been shown to reveal hyperechogenicity of the substantia nigra (SN) in Parkinsonian patients and in about 10% of healthy controls. It is hypothesized that SN hyperechogenicity in healthy subjects is a vulnerability marker for idiopathic Parkinson's disease (IPD). Although there is strong evidence that the echomarker results from increased local iron content, the exact pathophysiological mechanisms remain incompletely understood. Thus, prognostic impact can only be estimated. We examined 14 subjects with SN hyperechogenicity (SN+) (7 IPD patients and 7 controls) and 7 healthy controls without the echomarker (SN-) by a magnetic resonance imaging method (MRI; T2 relaxation times) known to reveal tissue inhomogeneity following abnormal iron content and by F-Dopa PET to assess nigrostriatal function.

Differential hippocampal and prefrontal-striatal contributions to instance-based and rule-based learning

It is a topic of current interest whether learning in humans relies on the acquisition of abstract rule knowledge (rule-based learning) or whether it depends on superficial item-specific information (instance-based learning). Here, we identified brain regions that mediate either of the two learning mechanisms by combining fMRI with an experimental protocol shown to be able to dissociate both learning mechanisms. Subjects had to learn object-position conjunctions in several trials and blocks. In a learning condition, either objects (Experiment 1) or positions (Experiment 2) were held constant within-blocks. In contrast to a control condition in which object-position conjunctions were trial-unique, a performance increase within and across-blocks was observed in the learning condition of both experiments. We hypothesized that within-block learning mainly relies on instance-based processes, whereas across-block learning might depend on rule-based mechanisms. A within-block parametric fMRI analysis revealed a learning-related increase of lateral prefrontal and striatal activity and a learning-related decrease of hippocampal activity in both experiments. By contrast, across-block learning was associated with an activation modulation in distinct prefrontal-striatal brain regions, but not in the hippocampus. These data indicate that hippocampal and prefrontal-striatal brain regions differentially contribute to instance-based and rule-based learning.

Prefrontal-hippocampal dynamics involved in learning regularities across episodes

Using functional magnetic resonance imaging, the neural correlates of context-specific memories and invariant memories about regularities across episodes were investigated. Volunteers had to learn conjunctions between objects and positions. In an invariant learning condition, positions were held constant, enabling subjects to learn regularities across trials. By contrast, in a context-specific condition object-position conjunctions were trial unique. Performance increase in the invariant learning condition was paralleled by a learning-related increase of inferior frontal gyrus activation and ventral striatal activation and a decrease of hippocampus activation. Conversely, in the context-specific condition hippocampal activation was constant across trials. We argue that the learning-related hippocampal activation pattern might be due to reduced relational binding requirements once regularities are extracted. Furthermore, we propose that the learning-related prefrontal modulation reflects the requirement to extract and maintain regularities across trials and the adjustment of object-position conjunctions on the basis of the extracted knowledge. Finally, our data suggest that the ventral striatum encodes the increased predictability of spatial features as a function of learning. Taken together, these results indicate a transition of the relative roles of distinct brain regions during learning regularities across multiple episodes: regularity learning is characterized by a shift from a hippocampal to a prefrontal-striatal brain system.

Monocular visual activation patterns in albinism as revealed by functional magnetic resonance imaging

Human albinism is characterized by a disturbance of the chiasmatic projection system leading to predominant representation of just one eye in the contralateral hemisphere. Patients show congenital nystagmus without perceiving oscillopsia. The purpose of the present study was to demonstrate the consequences of atypical chiasmatic crossing with monocular visual stimulation using functional magnetic resonance imaging (fMRI). Sixteen patients with albinism and fifteen normally pigmented controls were stimulated with a monocular visual activation paradigm using flickering checkerboards. In patients, we observed contralaterally dominated activation of visual cortices correlating to clinical albinism parameters. This confirms albinism as a continuous range of hypopigmentation disorders. Additionally, albinos showed activation of the superior colliculus and of visual motion areas although the stimulus was stationary. Activation of visual motion areas is due probably to congenital nystagmus without a conscious correlate like oscillopsia.

Configuration of the optic chiasm in humans with albinism as revealed by magnetic resonance imaging

PURPOSE

To determine whether the size and configuration of the optic chiasm in humans with albinism is different from that in normal control subjects.

METHODS

Seventeen patients and 15 control subjects underwent magnetic resonance imaging of the entire head. Images were reformatted to the chiasm region and analyzed with observer-independent morphometry and measurements by a blinded observer.

RESULTS

The albino group showed significantly smaller chiasmatic widths, smaller optic nerves and tracts, and wider angles between nerves and tracts. Statistical morphometry showed a different configuration of the optic chiasm.

CONCLUSIONS

Size and configuration of the optic chiasm in humans with albinism are distinctly different from those in normal control subjects and reflect the atypical crossing of optic fibers.