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S Mirzazade

Publications and source records attributed to S Mirzazade.

8 recordsLinked to original sources
PubMed2001

The role of the inferior parietal cortex in linking the tactile perception and manual construction of object shapes.

We employed functional magnetic resonance imaging (fMRI) in 12 healthy subjects to measure cerebral activation related to a set of higher order manual sensorimotor tasks performed in the absence of visual guidance. Purposeless manipulation of meaningless plasticine lumps served as a reference against which we contrasted two tasks where manual manipulation served a meaningful purpose, either the perception and recognition of three-dimensional shapes or the construction of such shapes out of an amorphous plasticine lump. These tasks were compared with the corresponding mental imagery of the modelling process which evokes the constructive concept but lacks concomitant sensorimotor input and output. Neural overlap was found in a bilateral activity increase in the posterior and anterior intraparietal sulcus area (IPS and AIP). Differential activation was seen in the supplementary and cingulate motor areas, the left M1 and the superior parietal lobe for modelling and in the left angular and ventral premotor cortex for imagery. Our data thus point to a congruent neural substrate for both perceptive and constructive object-oriented sensorimotor cognition in the AIP and posterior IPS. The leftward asymmetry of the inferior parietal activations, including the angular gyrus, during imagery of modelling along with the ventral premotor activations emphasize the close vicinity of the circuitry for cognitive manipulative motor behaviour and language.

Adult↗
PubMed2000

The effect of sequence repeat time on auditory cortex stimulation during phonetic discrimination.

Acoustic noise generated by the MR scanner gradient system during fMRI studies of auditory function is a very significant potential confound. Despite these deleterious effects, fMRI of the auditory cortex has been successful and numerous practitioners have circumvented the problem of acoustic masking noise. In the context of auditory cortex fMRI, the sequence repeat time (TR) has the effect of altering the length of time during which the scanner is quiet. Indeed, the move to whole-brain fMRI makes the problem of acoustic noise more acute and points to the need to examine the role of TR and its influence on the BOLD signal. The aim of this study was to examine the effect of varying the TR time on activation of auditory cortex during presentation and performance of a phonetic discrimination task. The results presented here demonstrate that the influence of sequence repeat time is considerable. For a short repeat time it is likely that the noise from the scanner is a significant mask and hinders accurate task performance. At the other extreme, a repeat time of 9 s is also suboptimal, probably due to attentional effects and lack of concentration and not least because of the longer overall measurement times. The results of this study point to a complicated interplay between psychophysical factors as well as physical parameters; attention, acoustic noise, total duration of the experiment, consideration of the volume of acquisition, and overall difficulty of the task have to be assessed and balanced. For the paradigm used here, the results suggest an optimal TR of around 6 s for a 16-slice acquisition.

Artifacts↗
PubMed2000

Recognition of emotional prosody and verbal components of spoken language: an fMRI study.

This study examined the neural areas involved in the recognition of both emotional prosody and phonemic components of words expressed in spoken language using echo-planar, functional magnetic resonance imaging (fMRI). Ten right-handed males were asked to discriminate words based on either expressed emotional tone (angry, happy, sad, or neutral) or phonemic characteristics, specifically, initial consonant sound (bower, dower, power, or tower). Significant bilateral activity was observed in the detection of both emotional and verbal aspects of language when compared to baseline activity. We found that the detection of emotion compared with verbal detection resulted in significant activity in the right inferior frontal lobe. Conversely, the detection of verbal stimuli compared with the detection of emotion activated left inferior frontal lobe regions most significantly. Specific analysis of the anterior auditory cortex revealed increased right hemisphere activity during the detection of emotion compared to activity during verbal detection. These findings illustrate bilateral involvement in the detection of emotion in language while concomitantly showing significantly lateralized activity in both emotional and verbal detection, in both the temporal and frontal lobes.

Adult↗
PubMed1999

The time course of the BOLD response in the human auditory cortex to acoustic stimuli of different duration.

The relationship between activity within the human auditory cortices and the duration of heard tones was investigated by measuring the hemodynamic response with functional magnetic resonance imaging. We demonstrate that there is no significant influence of stimulus duration as used here on the intensity and spatial extent of the hemodynamic response in the auditory cortices. We found however, that the time course of the hemodynamic response to the repeated stimulus presentation exhibited a characteristic decline after the first stimulus exposure during the activation period. The possible reasons for this time course are currently unknown, however, several factors may be involved, including top-down mechanisms and/or the interplay of tissue perfusion and oxygen consumption.

Acoustic Stimulation↗
PubMed1999

Attention modulates activity in the primary and the secondary auditory cortex: a functional magnetic resonance imaging study in human subjects.

Using functional magnetic resonance imaging, ten healthy subjects were scanned whilst listening to consonant-vowel syllables under three different conditions: (i) a 'no-attention' condition required subjects to ignore the stimuli; (ii) an 'attend' condition requiring attentive listening to stimuli; (iii) a 'detect' condition requiring detection of a specific target syllable. Hemodynamic responses were measured in the primary and secondary auditory cortex. These three conditions were associated with significantly different activations in the primary and secondary auditory cortex. The strongest activations were found for the 'detect' condition, followed by the 'attend' condition. The weakest activation was evident during the 'no-attention' condition. There were also stronger activations in the left hemisphere and within the primary auditory cortex. These results suggest that the primary and secondary auditory cortex play a main role in the selective attention.

Acoustic Stimulation↗
PubMed1999

The effect of finger-movement speed of the dominant and the subdominant hand on cerebellar activation: A functional magnetic resonance imaging study.

We studied the effects of different speeds of unimanual and bimanual movements on functional magnetic resonance signal changes in the cerebellum. Six healthy consistently right-handed subjects were scanned at rest and while executing a sequential finger-to-thumb-opposition task either unimanually (left or right hand) or bimanually. Movement frequency was paced by an auditory signal at rates of either 1 or 3 Hz. Significant frequency-dependent blood oxygen level-dependent signal increases were demonstrated ipsilaterally and contralaterally in the intermediate and lateral portions of the anterior cerebellum for bimanual movements and for unimanual movements with the subdominant hand. There was only a weak frequency-dependent effect for unimanual movements performed with the dominant hand. In addition, signals were stronger on the right intermediate zone of the anterior cerebellum for movements involving the right (dominant) hand while there was stronger activity on the left cerebellar hemisphere for movements involving the left (subdominant) hand. Taken together, these results suggest that rate and movement task effects on cerebellar activation are differentially sensitive to subdominant and dominant hand movements.

Adult↗
PubMed1998

A parametric analysis of the 'rate effect' in the sensorimotor cortex: a functional magnetic resonance imaging analysis in human subjects.

We studied the effects of different movement speeds of unimanual right hand movements on functional magnetic resonance signal changes in the sensorimotor cortex using echo planar imaging (EPI). Six healthy right-handed subjects were scanned at rest and while executing a finger tapping task with their right index finger. Movement frequency was visually paced at rates ranging from 0.5 to 5 Hz, separated by 0.5 Hz steps. The blood oxygen level dependent (BOLD) response within the left sensorimotor cortex was linearly and positively related to movement frequency. However, this relation holds (r2 = 0.91) only for movement frequencies faster than 1 Hz (1.5-5 Hz). For the slower frequencies there was an initial sharp increase of the BOLD response from 0.5 to 1 Hz followed by an activity drop for 1.5 Hz. These results are compatible with the idea that two different motor control modes are operative during slow or fast movements. During slow movements a computational demanding on-line feedback control mode is operative resulting in strong BOLD signals indicating extensive neural activity. During faster movements on the other hand a program-like motor control mode is operative resulting in less demanding neural computations. The amount of neural computation for the latter control mode increases with increasing movement speed.

Adult↗