ISSN:1065-9471    

DOI:10.1002/hbm.460030203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractNeural systems that participate in working memory for faces were investigated in an experiment designed to distinguish face perception areas from working memory areas. Regional cerebral blood flow (rCBF) was measured using positron emission tomography (PET) while subjects performed a sensorimotor control task, a face perception control task, and five working memory tasks with parametrically varied retention intervals, ranging from 1 to 21 sec. Striate and ventral occipitotemporal extrastriate areas demonstrated a simple negative correlation between rCBF and retention delay, indicating that these areas participate principally in perceptual operations performed during visual stimulation. By contrast, right and left frontal areas demonstrated rCBF increases that were significantly more sustained across delays than were increases in ventral extrastriate areas, but the relation between rCBF and retention interval differed significantly by hemisphere. Whereas right frontal rCBF showed a nonsignificant tendency to diminish at longer delays, left inferior frontal, middle frontal, and anterior cingulate cortex, as well as left parietal and inferior temporal cortex, demonstrated their largest rCBF increases at the longest delays. These results indicate that right frontal and left frontal, parietal, and temporal areas all participate in face working memory, but that left hemisphere areas are associated with a more durable working memory representation or strategy that subjects rely on increasingly with longer retention intervals. One possible explanation for this hemispheric difference is that left hemisphere activity is associated with a face representation that embodies the result of more analysis and elaboration, whereas right frontal activity is associated with a simpler, icon‐like image of a face that is harder to maintain in working memory. © 1995 Wiley‐Liss,

ISSN:1065-9471    

DOI:10.1002/hbm.460030204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractAlthough motor performance may be enhanced through mental practice, the neurophysiological substrate of mental stimulation (ideation) of a motor task is not well established. We used blood oxygen level‐dependent contrast echo planar imaging at 1.5 T to identify regions of increased neural activity during the performance and ideation of a motor task. Five subjects performed a sequential finger‐to‐thumb opposition task and also imagined themselves performing the task in the absence of actual muscle movement. In all subjects, the left primary sensorimotor cortex showed more activation with actual movement than with motor ideation, but two subjects had significant activation with motor ideation. The left premotor area showed comparable activation with both actual and imagined performance in three subjects. These findings support the involvement of the primary motor area as well as the premotor area in motor ideation. © 1995 Wiley‐L

ISSN:1065-9471    

DOI:10.1002/hbm.460030205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractBy several accounts, reading single words may be accomplished either by sequentially transcribing orthographic units into their corresponding sounds (an indirect route), or by directly associating a visual word form to the semantic or articulatory representation (a direct route). By contrast, the similar task of naming objects must rely only on a direct route, since objects cannot be “sounded out.” To study the localization of cognitive processes specific to reading, we used positron emission tomography (PET) to measure regional cerebral blood flow while subjects named words and pictures of objects silently or aloud. Group averages of blood flow changes were obtained for experimental vs. control tasks. Object and word presentations elicited similar blood flow increases in extra‐striate visual cortices compared with a visual noise control. Silent reading invoked a neural network very similar to that seen when subjects named objects silently, consistent with a “direct” route. Naming objects aloud produced the addition of motor output regions to this network. By contrast, oral reading produced a markedly different pattern of activated regions, suggesting reliance on a separate phonological pathway. These results provide support for the dual coding hypothesis in reading and challenge the use of strict hierarchical models of cognitive operations in PET activation studies. © 1995 Wiley

ISSN:1065-9471    

DOI:10.1002/hbm.460030206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractSubjects decided whether names were appropriate for accompanying pictures while their local cerebral blood flow was monitored using positron emission tomography (PET); in one condition, the names were at the “entry” level (i.e., the level spontaneously named, as in “bird” for a robin), in another condition they were at a superordinate level (e.g., “animal”), and in another they were at a subordinate level (e.g., “robin”). The results indicated that different processes are used to evaluate terms at the different levels of analysis. Specifically, there was evidence that memory search is used to evaluate superordinates, but one must collect additional perceptual information to evaluate subordinates. In addition, in another condition the subjects saw written words that named the entry‐level term and decided whether the object could be named by superordinate terms. Similar, but not identical, activation was observed as was found when subjects evaluated superordinate terms for pictures. © 19

ISSN:1065-9471    

DOI:10.1002/hbm.460030207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractWith the purpose of localising those anatomical structures participating in the discrimination of spatial frequencies and orientations of gratings, we measured regional cerebral blood flow (rCBF) changes with positron emission tomography (PET) and15O‐butanol as tracer in ten healthy young male volunteers. The subjects performed two‐alterative forced‐choice discriminations of pairs of squarewave gratings regarding their spatial frequencies or orientations (spatial frequency and orientation tasks) or pairs of a grating and a two‐dimensional random noise pattern regarding the presence or absence of grating pattern (reference task). In both the spatial frequency and orientation discrimination tasks a widely distributed network of functional fields is activated in the occipital, temporal, parietal, and frontal cortices and in the cerebellum. Spatial frequency discrimination required the activation of more cortical fields than orientation discrimination, and whereas the total volume of activated fields in temporal and frontal lobes were similar in the two tasks, the volumes of activated fields in the occipital lobes as well as in the parietal lobes were about two and a half times larger in spatial frequency discrimination than in orientation discrimination. The two networks of cortical fields were partially overlapping in the two tasks. The findings indicate that the discrimination of spatial frequency and orientation signals engages functional networks of cortical fields widely distributed in the human brain. Whereas both the occipito‐temporal and occipito‐parietal visual pathways are involved in both tasks, the processing and analysis of spatial frequency information activates occipital and parietal lobe regions more extensively than those of orientation information. © 1995 Wil

ISSN:1065-9471    

DOI:10.1002/hbm.460030208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractIn order to study brain activity associated with “incidental” cognitive processing, regional cerebral blood flow (rCBF) was measured in six volunteers while they monitored a sequence of pseudo‐words (e.g., FLOPE) for the rare occasions when the letters were displayed in blue rather than white. In the control condition, the same pseudo‐word was presented repeatedly. In one experimental condition all 60 pseudo‐words were different, while in the other there were 18 repetitions. Although it was not necessary to “read” the pseudo‐words to perform the monitoring task, subsequent forced choice recognition memory for these stimuli was significantly greater than chance. Furthermore, there were significant differences in blood flow between the three conditions. When different pseudo‐words were presented there was significantly greater activity in brain areas concerned with shape and object identity (extrastriate cortex bilaterally), with visual word form (left inferior temporal gyrus), and with articulatory word form (Broca's area) even though none of this information about the pseudo‐words was needed for performance of the monitoring task. In the condition in which some of the words were repeated, there was significantly reduced activity in the right lingual gyrus. This area may therefore be a possible anatomical locus for repetition priming with verbal stimuli. These results indicate the importance of taking into account incidental processing when designing tasks for functional imaging experiments. ©

ISSN:1065-9471    

DOI:10.1002/hbm.460030209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:1065-9471    

DOI:10.1002/hbm.460030202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY