Biomedical subjects

Katsuyuki Sakai

Publications and source records attributed to Katsuyuki Sakai.

7 recordsLinked to original sources

PubMed2003

Chunking during human visuomotor sequence learning.

Motor sequence learning is a process whereby a series of elementary movements is re-coded into an efficient representation for the entire sequence. Here we show that human subjects learn a visuomotor sequence by spontaneously chunking the elementary movements, while each chunk acts as a single memory unit. The subjects learned to press a sequence of 10 sets of two buttons through trial and error. By examining the temporal patterns with which subjects performed a visuomotor sequence, we found that the subjects performed the 10 sets as several clusters of sets, which were separated by long time gaps. While the overall performance time decreased by repeating the same sequence, the clusters became clearer and more consistent. The cluster pattern was uncorrelated with the distance of hand movements and was different across subjects who learned the same sequence. We then split a learned sequence into three segments, while preserving or destroying the clusters in the learned sequence, and shuffled the segments. The performance on the shuffled sequence was more accurate and quicker when the clusters in the original sequence were preserved than when they were destroyed. The results suggest that each cluster is processed as a single memory unit, a chunk, and is necessary for efficient sequence processing. A learned visuomotor sequence is hierarchically represented as chunks that contain several elementary movements. We also found that the temporal patterns of sequence performance transferred from the nondominant to dominant hand, but not vice versa. This may suggest a role of the dominant hemisphere in storage of learned chunks. Together with our previous unit-recording and imaging studies that used the same learning paradigm, we predict specific roles of the dominant parietal area, basal ganglia, and presupplementary motor area in the chunking.

Cluster Analysis↗

PubMed2003

Obstinate thrombosis during percutaneous coronary intervention in a case with heparin-induced thrombocytopenia with thrombosis syndrome successfully treated by argatroban anticoagulant therapy.

We describe a case of massive coronary thrombus after the coronary stenting due to heparin-induced thrombocytopenia with thrombosis syndrome (HITTS). Only argatroban was able to resolve the thrombus. This is the first case in which argatroban successfully treated massive thrombus during percutaneous coronary intervention in a patient with HITTS.

Angioplasty, Balloon, Coronary↗

PubMed2003

Prefrontal interactions reflect future task operations.

When task instructions are given, the human brain establishes a task set before the task is actually performed. By introducing a delay between the instruction and the task, we have identified the neural correlates of task sets using functional magnetic resonance imaging (fMRI). Subjects were instructed to remember a sequence of positions or letters, either in the order presented or in the reverse order. Spatial or verbal processing areas were active during the delay, depending on whether positions or letters were to be remembered, whereas the anterior region of the prefrontal cortex (PFC) was active regardless of the domain of the items. Furthermore, the nature of the interaction between the anterior PFC and the domain-specific posterior prefrontal areas (superior frontal sulcus and left inferior frontal gyrus) depended on whether the items were to be remembered in the forward or backward order. Thus we have identified inter-regional interactions that reflect preparation for task performance.

Adult↗

PubMed2003

Highly vascular pelvic tumor causing high-output heart failure because of massive arteriovenous shunting: a case report.

A 53-year-old Japanese woman underwent investigation of her heart murmur. A continuous abdominal bruit was heard. Blood gas analysis and chest X-ray showed congestive heart failure. Enhanced computed tomography of the pelvis showed a 10 x 4 cm hypervascular tumor in the retroperitoneal space. Cardiac catheterization disclosed a cardiac output of 13.2 L/min and a step-up of oxygen at the right common iliac vein. Abdominal aortic angiography showed an extremely vascular pelvic tumor and rapid filling of the inferior vena cava. This is a rare case of a highly vascular pelvic tumor causing high-output heart failure because of th massive arteriovenous shunting.

Arteriovenous Fistula↗

PubMed2002

Parahippocampal reactivation signal at retrieval after interruption of rehearsal.

Verbal information is maintained on-line within working memory by rehearsal. However, we still can recall the verbal information when rehearsal is interrupted. Here we show that this is achieved by reactivation of maintained information. We used event-related functional magnetic resonance imaging to identify brain activation at encoding, during memory delay, and at retrieval, within the same trial of a verbal working memory task. On half of the trials, retrieval was tested after arithmetic distraction to interrupt rehearsal of the remembered verbal items. We found that the parahippocampal cortex (PHC) was highly active at retrieval on trials with distraction compared with trials without distraction. The PHC did not show sustained activation during the memory delay. By contrast, the dorsolateral prefrontal cortex (DLPF), left superior temporal region (ST), and Broca's area showed sustained activation during the memory delay, suggesting their role in maintenance of verbal items. After arithmetic distraction, the DLPF and ST were engaged in arithmetic processing. Thus, these areas could not maintain the verbal items during the distraction. At retrieval of verbal items after the distraction, the DLPF, ST and Broca's area were also active. The activity was taken to reflect reactivated representation of the verbal items. The primary role of the PHC in retrieval may be to trigger the reactivation of these cortical areas that had maintained the remembered items, thereby reactivating the information that is no longer maintained on-line.

Adult↗

PubMed2002

Central mechanisms of motor skill learning.

Recent studies have shown that frontoparietal cortices and interconnecting regions in the basal ganglia and the cerebellum are related to motor skill learning. We propose that motor skill learning occurs independently and in different coordinates in two sets of loop circuits: cortex-basal ganglia and cortex-cerebellum. This architecture accounts for the seemingly diverse features of motor learning.

Animals↗

PubMed2002

Learning of sequences of finger movements and timing: frontal lobe and action-oriented representation.

Motor sequence learning involves learning of a sequence of effectors with which to execute a series of movements and learning of a sequence of timings at which to execute the movements. In this study, we have segregated the neural correlates of the two learning mechanisms. Moreover, we have found an interaction between the two learning mechanisms in the frontal areas, which we claim as suggesting action-oriented coding in the frontal lobe. We used positron emission tomography and compared three learning conditions with a visuo-motor control condition. In two learning conditions, the subjects learned either a sequence of finger movements with random timing or a sequence of timing with random use of fingers. In the third condition the subjects learned to execute a sequence of specific finger movements at specific timing; we argue that it was only in this condition that the motor sequence was coded as an action-oriented representation. By looking for condition by session interactions (learning vs. control conditions over sessions), we have removed nonspecific time effects and identified areas that showed a learning-related increment of activation during learning. Learning of a finger sequence was associated with an increment of activation in the right intraparietal sulcus region and medial parietal cortex, whereas learning of a timing sequence was associated with an increment of activation in the lateral cerebellum, suggesting separate mechanisms for learning effector and temporal sequences. The left intraparietal sulcus region showed an increment of activation in learning of both finger and timing sequences, suggesting an overlap between the two learning mechanisms. We also found that the mid-dorsolateral prefrontal cortex, together with the medial and lateral premotor areas, became increasingly active when subjects learned a sequence that specified both fingers and timing, that is, when subjects were able to prepare specific motor action. These areas were not active when subjects learned a sequence that specified fingers or timing alone, that is, when subjects were still dependent on external stimuli as to the timing or fingers with which to execute the movements. Frontal areas may integrate the effector and temporal information of a motor sequence and implement an action-oriented representation so as to perform a motor sequence accurately and quickly. We also found that the mid-dorsolateral prefrontal cortex was distinguished from the ventrolateral prefrontal cortex and anterior fronto-polar cortex, which showed sustained activity throughout learning sessions and did not show either an increment or decrement of activation.

Adult↗