Tormod Thomsen

Sex differences in visuo-spatial processing : An fMRI study of mental rotation

Following the theoretical framework of coordinate and categorical principals for visuo-spatial processing, originally formulated by [Kosslyn, S. M. (1987). Seeing and imagining in the cerebral hemispheres: AQ computational approach. Psychological Review, 94, 148-175], we present data from an fMRI study on mental rotation, using the classic [Shepard, R. N., & Metzler, J. (1971). Mental rotation of three-dimensional objects. Science, 171, 701-703] task, comparing males and females. Subjects were presented with black-and-white drawings of 3-D shapes taken from the set of 3-D perspective drawings developed by [Shepard, R. N., & Metzler, J. (1971). Mental rotation of three-dimensional objects. Science, 171, 701-703], alternated with 2-D white bars as control stimuli. The drawings were presented pairwise, as black and white drawings against a black circular background. On half of the trials, the two 3-D shapes were congruent but portrayed with different orientation, in the other half the two shapes were incongruent. Analysis of response accuracy and reaction times did not reveal any significant differences between the sexes. However, clusters of significant neuronal activation were found in the superior parietal lobule (BA 7), more intensely over the right hemisphere, and bilaterally in the inferior frontal gyrus (BA 44/45). Males showed predominantly parietal activation, while the females, in addition, showed inferior frontal activation. We suggest that males may be biased towards a coordinate processing approach, and females biased towards a serial, categorical processing approach.

Dichotic listening reveals functional specificity in prefrontal cortex: an fMRI study.

The present study used fMRI to investigate the relationship between stimulus presentation mode and attentional instruction in a free-report dichotic listening (DL) task with consonant-vowel (CV) syllables. Binaural and dichotic CV syllables were randomly presented to the subjects during four different instructional conditions: a passive listening instruction and three active instructions where subjects listened to both ears, right ear and left ear, respectively. The results showed that dichotic presentations activated areas in the superior temporal gyrus, middle and inferior frontal gyrus and the cingulate cortex to a larger extent than binaural presentations. Moreover, the results showed that increase of activation in these areas was differentially dependent on presentation mode and attentional instruction. Thus, it seems that speech perception, as studied with the DL procedure, involves a cortical network extending beyond primary speech perception areas in the brain, also including prefrontal cortex.

The effects of attention on speech perception: an fMRI study.

Focusing of attention to a specific speech source plays an important role in everyday speech perception. However, little is known of the neuronal substrates of focused attention in speech perception. Thus, the present study investigated the effects on neuronal activation of directed attention to auditory stimuli that differed in semantic content. Using an event-related fMRI protocol, single vowels, three-phoneme pseudowords and three- and four-phoneme real nouns and words were randomly presented to the subjects during four different instructional conditions. One condition was passive listening without any specific instructions of focusing of attention. The other conditions were attention focused on either the vowels, the pseudowords or the words. Thus, the acoustic stimulation was constant across conditions. The subjects were 13 healthy adults. Functional MRI was performed with a 1.5 T scanner, using an event-related design. During passive listening, there were significant activations bilaterally in the superior temporal gyrus. Instruction to attend to the pseudowords caused activation in middle temporal lobe areas, extending more anterior compared to the activations seen during passive listening. Instruction to attend to the vowel sounds caused an increase in activation in the superior/medial temporal lobe, with a leftward asymmetry. Instruction to attend to the words caused a leftward asymmetry, particularly in the middle and superior temporal gyri. It is concluded that attention plays a modulatory role in neuronal activation to speech sounds, producing specific activations to specific stimulus categories that may act to facilitate speech perception.

Brain localization of attentional control in different age groups by combining functional and structural MRI.

The present study used functional and structural MRI to investigate differences in neuronal substrates underlying shifts of attention in young and old subjects, studied with dichotic listening. Two different consonant-vowel syllables were presented and the subjects were instructed to attend to and report from either the left or right ear stimulus. Typically, a right-ear advantage is observed when attending to the right-ear stimulus, and a left-ear advantage when attending to the left-ear stimulus. The behavioral results showed that the old group had difficulties with attentional modulation of the right-ear advantage in the attend left condition. This is interpreted as a failure of an important aspect of attentional control; the top-down biasing of attention for selection of task-relevant stimulus. The fMRI results showed that an area in the left middle frontal gyrus was more activated in the young group compared to the old group in the attend left condition. The structural MRI data showed reduced gray matter density of the same area in the old group. Based on these converging findings, we suggest that the left middle frontal gyrus plays an important role in top-down biasing of selecting task-relevant stimuli, and to inhibit processing of task-irrelevant stimuli. To our knowledge, this is one of the first studies addressing the question on how age-related changes in attentional processing is reflected in both functional and structural differences in the brain.

Brain correlates of sentence translation in Finnish-Norwegian bilinguals.

We measured brain activation with functional magnetic resonance imaging (fMRI) while Finnish–Norwegian bilinguals silently translated sentences from Finnish into Norwegian and decided whether a later presented probe sentence was a correct translation of the original sentence. The control task included silent sentence reading and probe sentence decision within a single language, Finnish. The translation minus control task contrast activated the left inferior frontal gyrus (Brodmanns area 47) and the left basal ganglia. The left inferior frontal activation appears to be related to active semantic retrieval and the basal ganglia activation to a general action control function that works by suppressing competing responses.

Honig's model of working memory and brain activation: an fMRI study.

The present study investigated changes in neuronal activation with fMRI related to Honigs model of working memory, which is much less studied compared with other working memory models. In contrast to other studies which have applied recognition procedures, the primary aim with the present study was to examine brain activation when subjects had to continuously recall and forget items held in working memory. The results showed that the mid-ventrolateral frontal cortex was particularly activated in the left hemisphere, whereas the mid-dorsolateral frontal cortex was particularly activated in the right hemisphere during execution of the working memory task. The findings are discussed in relation to process- and domain-specific accounts of working memory.

Different Brain Areas Activated during Imagery of Painful and Non-painful ‘Finger Movements’ in a Subject with an Amputated Arm

The purpose of the present study was to investigate differences in brain activation with functional magnetic resonance imaging (fMRI) during imagery of painful and non-painful ‘finger movements’ and ‘hand positioning’ in a subject with an amputated arm. The subject was a right-handed man in his mid-thirties who lost his right arm just above the elbow in a car-train accident. MRI was performed with a 1.5 T Siemens Vision Plus scanner. The basic design involved four conditions: imagining ‘painful finger movements’, ‘non-painful finger movements’, ‘painful hand positioning’, ‘non-painful hand positioning’. Imagery of finger movements uniquely activated the contralateral primary motor cortex which contains the classic ‘hand area’. The lateral part of the anterior cerebellar lobe was also activated during imagery of finger movements. Imagery of pain uniquely activated the somatosensory area, and areas in the left insula and bilaterally in the ventral posterior lateral nucleus of the thalamus. It is suggested that the insula and thalamus may involve neuronal pathways that are critical for mental processing of pain-related experiences, which may relate to a better understanding of the neurobiology of phantom limb pain.

Frontoparietal activation during delayed visuospatial recall in patients with epilepsy due to hippocampal sclerosis

We hypothesized that brain activation during encoding and retrieval of visual material differed between epilepsy patients with hippocampal sclerosis (HS) and healthy controls. Eleven patients with epilepsy and HS and nine age- and education-matched control subjects were tested during functional MRI recording. A three-block design for visuospatial memory encoding and retrieval and an interference interval longer than 1 minute without memory tasks were used. All subjects revealed parietal, occipital, and prefrontal activation patterns during encoding. Interference revealed parietal more than occipital activation, whereas retrieval revealed asymmetrical frontal and parietal activation. Patients demonstrated a relative increase in occipitoparietal versus frontal cortical activation as compared with controls. Memory performance did not differ between patients and controls. The increased activation in occipitoparietal versus frontal areas in the patients suggests cortical reorganization of visuospatial recognition memory in epilepsy patients with HS. The study is limited by other factors that may contribute to the results, for example, antiepileptic drugs, effects of greater cognitive effort allocated in patients than controls, and possibly subclinical epileptic activity. However, normal visuospatial memory performance in our patients with HS suggests successful network plasticity.

Plug & Play fMRI

965 popular. Nowadays, the real-time fMRI analyses could be performed on the MR-scanner itself . Those optional software packages are allowing a statistical analysis during or directly after the measurement. This enables the fMRI investigator, not only to explore the active brain areas, but also to decide whether an additional scan would be needed, in case of large movements or low BOLD signals. Those essential decisions are important for the success of an fMRI study, and should be made before the patient has left the scanner. This simplifies the scanning procedure and saves time, especially in a clinical environment. An offline analysis, using common functional imaging software could complete the individual picture of the patient’s diseases and abilities. To facilitate the performance of a clinical fMRI study, we developed an easy-to-use presentation tool, simplifying the scanning and presentation procedure by an automated synchronization of MR-scanner and stimulus PC, which is running the presentation of the tasks and collecting the subject’s responses. Introduction

The effects of attention on speech perception: An fMRI study

Focusing of attention to a specific speech source plays an important role in everyday speech perception. However, little is known of the neuronal substrates of focused attention in speech perception. Thus, the present study investigated the effects on neuronal activation of directed attention to auditory stimuli that differed in semantic content. Using an event-related fMRI protocol, single vowels, three-phoneme pseudowords and three- and four-phoneme real nouns and words were randomly presented to the subjects during four different instructional conditions. One condition was passive listening without any specific instructions of focusing of attention. The other conditions were attention focused on either the vowels, the pseudowords or the words. Thus, the acoustic stimulation was constant across conditions. The subjects were 13 healthy adults. Functional MRI was performed with a 1.5 T scanner, using an event-related design. During passive listening, there were significant activations bilaterally in the superior temporal gyrus. Instruction to attend to the pseudowords caused activation in middle temporal lobe areas, extending more anterior compared to the activations seen during passive listening. Instruction to attend to the vowel sounds caused an increase in activation in the superior/medial temporal lobe, with a leftward asymmetry. Instruction to attend to the words caused a leftward asymmetry, particularly in the middle and superior temporal gyri. It is concluded that attention plays a modulatory role in neuronal activation to speech sounds, producing specific activations to specific stimulus categories that may act to facilitate speech perception.