Mathias Bartels

Towards a functional neuroanatomy of self processing: effects of faces and words

We studied the neural correlates of self vs. non-self judgements using functional magnetic resonance imaging (fMRI). Individually tailored faces and personality trait words were used as stimuli in three experiments (exp.). In the first two experiments, brain activation was measured while subjects viewed morphed versions of either their own (self face exp.) or their partners face (partners face exp.), alternating in blocks with presentation of an unknown face. In the self face exp. right limbic areas (hippocampal formation, insula, anterior cingulate), the right middle temporal lobe, left inferior parietal and left prefrontal regions showed signal changes. In the partners face exp., only the right insula was activated. In the third exp., subjects made decisions about psychological trait adjectives previously categorized as describing their own attributes. Activation was present in the precuneus, the left parietal lobe, left insula/inferior frontal gyrus and the left anterior cingulate. A reaction time advantage was present when subjects responded to self-relevant words. The main area with signal changes during self-reference processing, regardless of the type of stimulus, was the left fusiform gyrus. The self-relevant stimuli engaged to a differential extent long term and working memory, semantic and emotional processes. We suggest that regions activated by these stimuli are engaged in self-processing.

Recognizing one's own face

We report two studies of facial self-perception using individually tailored, standardized facial photographs of a group of volunteers and their partners. A computerized morphing procedure was used to merge each target face with an unknown control face. In the first set of experiments, a discrimination task revealed a delayed response time for the more extensively morphed self-face stimuli. In a second set of experiments, functional magnetic resonance imaging (fMRI) was used to measure brain activation while subjects viewed morphed versions of either their own or their partners face, alternating in blocks with presentation of an unknown face. When subjects viewed themselves (minus activation for viewing an unknown face), increased blood oxygenation was detected in right limbic (hippocampal formation, insula, anterior cingulate), left prefrontal cortex and superior temporal cortex. In the partner (versus unknown) experiment, only the right insula was activated. We suggest that a neural network involving the right hemisphere in conjunction with left-sided associative and executive regions underlies the process of visual self-recognition. Together, this combination produces the unique experience of self-awareness.

The neural correlates of perceiving one's own movements

Feedforward mechanisms are important for movement control. They may also contribute to the identification of self-produced actions by attenuating the sensory consequences of self-produced movements. In our study, subjects opened and closed their hand slowly and continuously (0.5 Hz). This movement was filmed with an MRI compatible video camera and projected online onto a screen, viewed by the subject while BOLD contrast was measured with fMRI. The temporal delay between movement and feedback was parametrically varied (0-200 ms). In each trial, subjects judged whether there was a delay or not. There was a positive correlation between the extent of the temporal delay and activation in the right posterior superior temporal cortex (pSTS) and a negative correlation in the left putamen. A second analysis addressed the neural correlates of subjective judgement under conditions of uncertainty. This contrast showed a differential activation in the cerebellum. These results support the assumption of a forward model implying that predictions generated in motor areas attenuate sensory areas. They also suggest that efference copy mechanisms are not located within specific brain areas but are implemented as a specific form of interaction between perceptual and motor areas depending on the modalities and the type of actions involved. Further, conscious detection of small temporal deviations might be based on signals generated in the cerebellum which provide fine-grained temporal information. These results might be useful to refine theories about the role of forward mechanisms in the emergence of disorders of the self, such as in schizophrenia.

Transient suppression of tinnitus by transcranial magnetic stimulation.

It has been proposed that tinnitus is associated with an irregular activation of the temporoparietal cortex. If this activity is a functionally relevant component of the tinnitus‐related network, a virtual temporary lesion of this area should result in transient reduction of tinnitus. To test this hypothesis, we applied 10Hz repetitive transcranial magnetic stimulation to eight scalp and four control positions in 14 patients with chronic tinnitus. Stimulation of left temporoparietal cortex significantly reduced tinnitus (Friedman analysis of variance, p < 0.05; compared with control), indicating that secondary auditory areas can be critical for tinnitus perception, perhaps as a consequence of maladaptive cortical reorganization. Ann Neurol 2003

Differential activation in parahippocampal and prefrontal cortex during word and face encoding tasks.

Episodic encoding is the first step in the formation of a memory trace. The relation between type of stimulus material and regional brain activation is not fully understood. We measured brain activation using fMRI in 12 healthy subjects during two experiments, word and face encoding. A widespread network of common activations in both tasks was present in the bilateral frontal (BA44/45), occipital (BA17/18/19) and fusiform gyri (BA37) as well as the right hippocampal formation (BA30). A region-of-interest-analysis for the hippo- campal formation and dorsolateral prefrontal cortex (DLPFC) was performed additionally. During face encoding the right dorsal and during word encoding the bilateral ventral hippocampal region was activated. In the prefrontal cortex a lateralization to the left side was present only for word encoding. During encoding, activation in the inferior frontal and hippocampal cortex is modulated by the type of stimulus material.

Enhancement of human cortico-motoneuronal excitability by the selective norepinephrine reuptake inhibitor reboxetine

It has been proposed that norepinephrine plays a critical role in the modulation of cortical excitability, which in turn is thought to influence functional recovery from brain lesions. The purpose of the present experiments was to determine if it is possible to modulate cortical excitability with the selective norepinephrine reuptake inhibitor reboxetine in intact humans. Recruitment curve and intracortical facilitation, assessed by transcranial magnetic stimulation, were increased after oral intake of 8 and 4 mg reboxetine, in the absence of changes in motor threshold, intracortical inhibition, M-response, F-wave or H-reflex. These results demonstrate that reboxetine enhances cortical excitability and raise the possibility that it could act as a plasticity enhancing substance potentially useful in combination with neurorehabilitative strategies geared to enhance neurorehabilitation.

Pausing for thought: Engagement of left temporal cortex during pauses in speech

Pauses during continuous speech, particularly those that occur within clauses, are thought to reflect the planning of forthcoming verbal output. We used functional Magnetic Resonance Imaging (fMRI) to examine their neural correlates. Six volunteers were scanned while describing seven Rorschach inkblots, producing 3 min of speech per inkblot. In an event-related design, the level of blood oxygenation level dependent (BOLD) contrast during brief speech pauses (mean duration 1.3 s, SD 0.3 s) during overt speech was contrasted with that during intervening periods of articulation. We then examined activity associated with pauses that occurred within clauses and pauses that occurred between grammatical junctions. Relative to articulation during speech, pauses were associated with activation in the banks of the left superior temporal sulcus (BA 39/22), at the temporoparietal junction. Continuous speech was associated with greater activation bilaterally in the inferior frontal (BA 44/45), middle frontal (BA 8) and anterior cingulate (BA 24) gyri, the middle temporal sulcus (BA 21/22), the occipital cortex and the cerebellum. Left temporal activation was evident during pauses that occurred within clauses but not during pauses at grammatical junctions. In summary, articulation during continuous speech involved frontal, temporal and cerebellar areas, while pausing was associated with activity in the left temporal cortex, especially when this occurred within a clause. The latter finding is consistent with evidence that within-clause pauses are a correlate of speech planning and in particular lexical retrieval.

Self-regulation of slow cortical potentials in psychiatric patients: Schizophrenia

Slow cortical potentials (SCPs) are considered to reflect the regulation of attention resources and cortical excitability in cortical neuronal networks. Impaired attentional functioning, as found in patients with schizophrenic disorders, may covary with impaired SCP regulation. This hypothesis was tested using a self-regulation paradigm. Twelve medicated male schizophrenic inpatients and 12 healthy male controls received continuous feedback of their SCPs, during intervals of 8 s each, by means of a visual stimulus (a stylized rocket) moving horizontally across a TV screen. The position of the feedback stimulus was a linear function of the integrated SCP at each point in time during the feedback interval. Subjects were required to increase or reduce negative SCPs (referred to pretrial baseline) depending on the presentation of a discriminative stimulus. The correct response was indicated by the amount of forward movement of the feedback stimulus and by monetary rewards. Schizophrenics participated in 20 sessions (each comprising 110 trials), while controls participated in 5 sessions. Compared with the healthy controls, schizophrenics showed no significant differentiation between negativity increase and negativity suppression during the first sessions. However, in the last 3 sessions, patients achieved differentiation similar to controls, demonstrating the acquisition of SCP control after extensive training.

Noradrenergic modulation of human cortex excitability by the presynaptic α2-antagonist yohimbine

The objective of this study was to determine if yohimbine, a central norepinephrine enhancing drug, increases cortico-motoneuronal excitability in intact humans. Transcranial magnetic stimulation was used to assess excitability of the motor system reflected in the parameters motor threshold, recruitment curve, intracortical inhibition and intracortical facilitation before and after oral administration of 20 and 40 mg yohimbine. Oral intake of 40 but not 20 mg yohimbine increased slope and plateau of the recruitment curve and intracortical facilitation. Motor threshold and intracortical inhibition remained unchanged. The data show that pharmacological enhancement of central norepinephrine in humans is effective to increase the cortico-motoneuronal excitability. Since cortical excitability is closely linked to neuroplasticity, this observation might be of possible relevance for strategies to enhance rehabilitative processes after cortical lesions by pairing noradrenergic drugs with motor training.

Computerized tomography in tardive dyskinesia

SummaryTwenty-nine patients with moderate to severe tardive dyskinesia (TD) and 29 age-and sex-matched controls (C) with long-term neuroleptic therapy comparable to that of the patients were all examined using computeized tomography. Significant differences were found between the two groups in the width of the third ventricle (TD>C), the bicaudate distance (TD>C), the computed area of the head of the caudate nucleus (TD<C), and the area of the lenticular nucleus (TD<C). No significant differences were established in the ventricular or cella media indices. These results suggest that structural abnormalities, primarily in the basal ganglia system, are present in TD patients. Psychological testing with the Benton visual retention test also showed significant differences with regard to cerebro-organic functional impairment among TD patients.