Functional MRI evidence for a role of frontal and inferior temporal cortex in amodal components of priming.
(25/1550)
Changes in human brain activity associated with repetition priming during word generation were characterized across a series of neuroimaging and behavioural studies. Repetition priming was consistently observed behaviourally as a decrease in response latency for repeated items, and was found for both visually and aurally cued word-generation tasks. Brain imaging using whole-brain functional MRI identified neural correlates of these effects. The principal effect of priming was to reduce neural activity within regions that were already being used to perform the word-generation tasks. Repeated word generation in response to visual cues was correlated with anatomically selective reductions in activity within the left frontal cortex along the inferior frontal gyrus and inferior temporal regions and, to a lesser degree, in specific earlier visual regions. These reductions were reversed when new items were presented, indicating that they were item-specific. Repeated word generation in response to aural cues also showed anatomically selective activity reductions within the left frontal and inferior temporal regions, indicating that these activity reductions were not dependent on the perceptual modality of the cue. The auditory cortex showed minimal repetition-related reductions. The presence of activity within left frontal regions that decreases as a function of item repetition for both visual and auditory cues suggests that these reductions may underlie an amodal repetition-priming effect existing at processing stages involving lexical/semantic search and access. The surprising finding that activity reductions in the inferior temporal cortex can be linked to repetition of either visual or auditory cues further suggests that these regions may be modulated in a top-down fashion during repetition priming, independent of (or in parallel with) stimulus-driven perceptual processes. Taken collectively, the data converge on a neural correlate of lexical/semantic priming. Amodal lexical/semantic processes, which may be triggered initially by modality-specific cues, proceed via an interaction between frontal and posterior brain regions. These interdependent regions show activity reductions that correlate with facilitated task performance when items are repeated. (+info)
Functional asymmetry of human prefrontal cortex: encoding and retrieval of verbally and nonverbally coded information.
(26/1550)
There are several views about the organization of memory functions in the human prefrontal cortex. One view assumes a process-specific brain lateralization according to different memory subprocesses, that is, encoding and retrieval. An alternative view emphasizes content-specific lateralization of brain systems involved in memory processes. This study addresses this apparent inconsistency between process- and content-specific lateralization of brain activity by investigating the effects of verbal and nonverbal encoding on prefrontal activations during encoding and retrieval of environmental novel sounds using fMRI. An intentional memory task was applied in which subjects were required either to judge the sounds' loudness (nonverbal encoding task) or to indicate whether or not a sound can be verbally described (verbal encoding task). Retrieval processes were examined in a subsequent yes/no recognition test. In the study phase the right posterior dorsolateral prefrontal cortex (PFC) was activated in both tasks. During verbal encoding additional activation of the left dorsolateral PFC was obtained. Retrieval-related fMRI activity varied as a function of encoding task: For the nonverbal task we detected an activation focus in the right posterior dorsolateral PFC whereas an activation in the left dorsolateral PFC was observed for the verbal task. These findings indicate that the right dorsolateral PFC is engaged in encoding of auditory information irrespective of encoding task. The lateralization of PFC activity during retrieval was shown to depend on the availability of verbal codes, with left hemispheric involvement for verbally and right hemispheric activation for nonverbally coded information. (+info)
Treatment outcome in cleft lip and palate: issues and perspectives.
(27/1550)
In the last 40 years, great progress has been made toward a better understanding of many aspects of the cleft lip and palate defect, but there is still a long way to go before there is agreement on the optimal treatment procedures. With regard to the primary operations, it can be stated, in a somewhat simplified form, that there are two main schools of thought in cleft treatment. One advocates early closure of the lip and palate, a procedure which imparts a high priority to early speech function. The other recommends delayed closure of the hard palate, thereby according a high priority to the growth of the maxilla. A number of intercenter and multicenter studies have been carried out recently in an effort to elucidate which procedures give the best result, both esthetically and functionally. The results are ambiguous, and this has led a number of researchers to suggest that the randomized clinical trial is the only way to resolve the ambiguity. The fact that it has proved difficult to identify the optimal procedures in the field of cleft lip and palate treatment need not only be due to a less than optimal research design; a contributory factor might also be the great variability in craniofacial morphology and in the response to treatment in patients who have exactly the same cleft lip and palate diagnosis. Intensive research has made it possible to state categorically that clefts occur due to many different factors in an interplay between genetics and environment. Therefore, it is not likely that a single gene can be responsible for clefting. Since scar tissue presents many problems-for instance, impairment of growth-the reduction or prevention of scar formation has long been a desirable goal. The discovery that a fetus can heal without scar formation has led to many animal experiments. The timing of the surgical intervention on fetuses is critical, since late-gestation fetuses heal with adult-like scarring. There are still many unsolved problems connected with fetal surgery, and at present prenatal surgery for repair of cleft lip and palate is not ethically defensible in humans. On the other hand, it appears that there are considerable possibilities for the reduction of human scarring after surgery with the introduction of various wound-healing medications. (+info)
On the origin of internal structure of word forms.
(28/1550)
This study shows that a corpus of proto-word forms shares four sequential sound patterns with words of modern languages and the first words of infants. Three of the patterns involve intrasyllabic consonant-vowel (CV) co-occurrence: labial (lip) consonants with central vowels, coronal (tongue front) consonants with front vowels, and dorsal (tongue back) consonants with back vowels. The fourth pattern is an intersyllabic preference for initiating words with a labial consonant-vowel-coronal consonant sequence (LC). The CV effects may be primarily biomechanically motivated. The LC effect may be self-organizational, with multivariate causality. The findings support the hypothesis that these four patterns were basic to the origin of words. (+info)
Effects of tryptophan depletion on anxiety induced by simulated public speaking.
(29/1550)
Several lines of evidence point to the participation of serotonin (5HT) in anxiety. Its specific role, however, remains obscure. The objective of the present study was to evaluate the effect of reducing 5HT-neurotransmission through an acute tryptophan depletion on anxiety induced by a simulated public speaking (SPS) test. Two groups of 14-15 subjects were submitted to a 24-h diet with a low or normal content of tryptophan and received an amino acid mixture without (TRY-) or with (TRY+) tryptophan under double-blind conditions. Five hours later they were submitted to the SPS test. The state-trait anxiety inventory (STAI) and the visual analogue mood scale (VAMS) were used to measure subjective anxiety. Both scales showed that SPS induced a significant increase in anxiety. Although no overall difference between groups was found, there was a trend (P = 0.078) to an interaction of group x gender x phases of the SPS, and a separate analysis of each gender showed an increase in anxiety measured by the STAI in females of the TRY- group. The results for the female TRY- group also suggested a greater arousing effect of the SPS test. In conclusion, the tryptophan depletion procedure employed in the present study did not induce a significant general change in subjective anxiety, but tended to induce anxiety in females. This suggests a greater sensitivity of the 5HT system to the effects of the procedure in this gender. (+info)
The parent-physician relationship in pediatric asthma care.
(30/1550)
OBJECTIVE: To examine the feasibility of using a behavioral coding system, the Five Minute Speech Sample (FMSS), to estimate the prevalence of relationship difficulties between parents and physicians in a pediatric asthma care setting. METHOD: The FMSS was administered to 20 parents of children with severe, chronic asthma and to the physicians they worked with during a brief day program admission. RESULTS: Rates of relationship difficulties between parents and physicians ranged from 15% to 40%, comparable to those previously identified in patient-therapist relationships in psychiatric populations. CONCLUSIONS: Although further information is needed about validity and reliability, the FMSS appears to provide clinically relevant information about the parent-physician relationship in the context of pediatric chronic illness. (+info)
Single word reading in developmental stutterers and fluent speakers.
(31/1550)
Ten fluent speakers and nine developmental stutterers read isolated nouns aloud in a delayed reading paradigm. Cortical activation sequences were mapped with a whole-head magnetoencephalography system. The stutterers were mostly fluent in this task. Although the overt performance was essentially identical in the two groups, the cortical activation patterns showed clear differences, both in the evoked responses, time-locked to word presentation and mouth movement onset, and in task-related suppression of 20-Hz oscillations. Within the first 400 ms after seeing the word, processing in fluent speakers advanced from the left inferior frontal cortex (articulatory programming) to the left lateral central sulcus and dorsal premotor cortex (motor preparation). This sequence was reversed in the stutterers, who showed an early left motor cortex activation followed by a delayed left inferior frontal signal. Stutterers thus appeared to initiate motor programmes before preparation of the articulatory code. During speech production, the right motor/premotor cortex generated consistent evoked activation in fluent speakers but was silent in stutterers. On the other hand, suppression of motor cortical 20-Hz rhythm, reflecting task-related neuronal processing, occurred bilaterally in both groups. Moreover, the suppression was right-hemisphere dominant in stutterers, as opposed to left-hemisphere dominant in fluent speakers. Accordingly, the right frontal cortex of stutterers was highly active during speech production but did not generate synchronous time-locked responses. The speech-related 20-Hz suppression concentrated in the mouth area in fluent speakers, but was evident in both the hand and mouth areas in stutterers. These findings may reflect imprecise functional connectivity within the right frontal cortex and incomplete segregation between the adjacent hand and mouth motor representations in stutterers during speech production. A network including the left inferior frontal cortex and the right motor/premotor cortex, likely to be relevant in merging linguistic and affective prosody with articulation during fluent speech, thus appears to be partly dysfunctional in developmental stutterers. (+info)
A systematic study of visual extinction. Between- and within-field deficits of attention in hemispatial neglect.
(32/1550)
Mechanisms of visual extinction were investigated in four patients with right hemisphere damage using a partial report paradigm. Different shapes (star or triangle) were displayed in one, two or four possible locations so that double simultaneous stimuli occurred either across the two hemifields or within the same hemifield. Patients attended either to the location (right, left or both), number (one, two or four) or shape (no, one or two stars among the shapes presented) of stimuli in three separate experiments using the same displays and exposure duration. Reporting the location (Experiment 1) produced marked contralesional extinction, although reaction time was delayed compared with unilateral right trials, indicating unconscious processing. Reaction time was also delayed on correct bilateral and unilateral left trials. In contrast, enumerating stimuli (Experiment 2) caused no significant contralesional extinction on bilateral displays and reaction time was similar on bilateral and unilateral right trials, suggesting that information from both fields was grouped in a single numerable percept in this task. However, patients often detected only one of two stimuli within the left field. Whereas similarity of shapes improved localization and did not affect enumeration, identifying stars among shapes (Experiment 3) revealed a severe inability to detect two similar targets between hemifields as well as within each of the hemifields. Distracting triangles were generally less detrimental to the perception of a concurrent target on either side, but slowed the reaction time regardless of whether they were in the same or the opposite field. Relative difficulty in ignoring distractors correlated with neglect severity on a cancellation task, and was most prominent in one patient with a large amount of frontal damage. These findings suggest that (i) allocation of attention to identical stimuli can be modulated by task demand; (ii) enumerating a small set of items across fields may not require attending to individual stimuli but relies on preattentive subitizing ability, as found in normal subjects; (iii) location information may be critical for attentional mechanisms subserved by the parietal cortex and pathological competition for awareness in extinction; (iv) extinction entails a bilateral deficit in attending to two concurrent similar targets when their features must be identified; and (v) the relevance of the stimuli can modulate the distribution of attention, possibly through frontal top-down control. These findings are consistent with recent neurophysiological evidence of parietal and frontal attentional influences on ventral visual pathways. (+info)