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How the brain handles distraction during working memory processing
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Abstracts / International Journal of Psychophysiology 77 (2010) 206–238
items during encoding of visuospatial locations. A strong targetrelated theta response predicts high visual working memory capacity, whereas a strong response of this theta network to encoding of distracting items predicts low memory capacity. During maintenance of visual items, on the other hand, sustained cross-frequency phase coupling between theta and gamma (50–70 Hz) is obtained at brain areas storing target items. This theta–gamma phase coupling shows a load-dependent increase of up to four items to be retained. When memory load is further increased, theta and gamma phases are decoupled again. The magnitude of memory load-dependent theta– gamma phase coupling predicts individual working memory capacity. Efficient suppression of distracter items during a retention period, however, is reflected by increased EEG alpha (8–12 Hz) amplitude at brain areas processing distracting visual information. Memory capacity can also be predicted by alpha amplitude, in this case, based on the efficient inhibition of distracter maintenance. Moreover, by entraining alpha activity using repetitive TMS, it can be shown that memory capacity is increased as the neural mechanism of distracter suppression is reinforced by the stimulation. doi:10.1016/j.ijpsycho.2010.06.010
Frequency-selective generators of oscillatory brain activity allow identifying processes of a working memory Nina N. Danilovaa, Elena A. Strabykinab a Department of Psychology, Lomonosov Moscow State University, Russia b Department of Computational Mathematics and Cybernetics, Lomonosov Moscow State University, Russia The aim of this study to investigate processes of visual working memory by a new method of micro structural analysis of event-related oscillations based on the pacemaker hypothesis of rhythm genesis (Danilova, 2006, 2008). Computation of equivalent current dipoles based on multichannel EEG data and their superposition onto slices of structural MRI for an individual human brain was used to identify localization of activated frequency-selective gamma (30-75 Hz), beta (14-29 Hz) and theta (4-7 Hz) generators. In experiments with working memory (10 participants), the subject has to memorize four pairs of two-digit numbers that are visually-presented and retain them during a delay interval for the subsequent comparison with target and no-target stimuli and performing motor reaction on target stimuli. The similarity of activated brain structures was found for the perception stage and retention interval. High-frequency generators were localized in frontal, associative (temporal, parietal) cortex, visual cortex, and cerebellum. Activity level in the frontal area during the perception and number memorization was higher than during the retention interval. However, during the delay period, the maximum activity of highfrequency generators was shifting from a frontal to an associative cortex and the cerebellum. The growth of cerebellum activity and the activation of visual cortex may be attributed to a motor readiness, the ability to predict the moment of stimulus presentation, and activating sensory memory traces. The investigation of the dynamic of memory retention showed that frequency-selective gamma and beta generators operating at different frequencies form bursts of join activity which periodically appears and disappears. The join activity of the frontal brain area with the visual and temporal cortex occurs during the delay interval and is absent at the perception stages. This suggests that during the retention interval, there is the interaction of local neuron networks represented by activated high-frequency generators. It facilitates rewriting the numerical information (LT-memory traces) from associative brain areas into prefrontal cortex, where it assumes an active form for subsequent use in behavior. Because theta rhythm is connected with encoding function, we have investigated the integra-
tion frequency-selective theta generators with high-frequency gamma and beta generators. For this aim, we used weighed centroid method for clusterization of neural sources in the dipole model of the brain. Results supported periodic fluctuations of join activity of gamma, beta, and theta generators. Localization of centroids showed repeated join activity in the prefrontal and/or cingular cortex, temporal, visualparietal cortex, cerebellum and thalamus. Our finding highlights the role of frequency-selective generators in the sub-function of visual working memory – the retention of memory traces in active form for future use in behavior. Research was supported by Russian Humanitarian Scientific Fund project No 10-06 00481а. doi:10.1016/j.ijpsycho.2010.06.011
How the brain handles distraction during working memory processing Synnöve Carlsona,b, Yuanye Mac Brain Research Unit, Low Temperature Laboratory, Aalto University School of Science and Technology, Espoo, Finland b Neuroscience Unit, Institute of Biomedicine/Physiology, University of Helsinki, Finland c Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China a
Distraction tends to impair working memory (WM) performance, but the underlying neuronal mechanisms are not clear. Here two studies are described in which the role of the prefrontal cortex (PFC) in the handling of distraction was investigated. In the first study, we investigated the effects of visual and auditory distraction on single neuron activity in the monkey PFC. Intracortical microelectrode recordings were conducted in two monkeys (Macaca mulatta) trained to perform visual and auditory spatial delayed-matching-to-sample (DMTS) tasks. Visual or auditory distracters were presented randomly during the delay period of the memory task. Distracters impaired WM task performance and affected the PFC neuronal activity. Distraction that was of the same sensory modality as the memorandum was more likely to impair WM performance and interferes with memory-related neuronal activity than distracters that were of a different sensory modality. The study also shows that neurons that are not involved in memory processing in less demanding conditions may become engaged in WM processing in more demanding conditions, thus suggesting that the PFC has mechanisms that help compensate for disruptive effects of external distracters. In the second study, we recorded auditory evoked potentials (AEPs) to task-irrelevant sounds in the PFC and parietal cortex (PC) of three monkeys (M. mulatta) while they performed a visual DMTS task; taskirrelevant sounds were presented during the WM processing and the intertrial intervals (ITI). The amplitudes of the AEPs in the PFC and PC to task-irrelevant tones were larger during the ITI than during WM processing. AEPs were also recorded in the PC after either a local anesthetic (procaine) or saline was injected intracortically bilaterally in the PFC. AEPs recorded in the PC to the sounds after the procaine injection were larger compared to the AEPs recorded after saline injections. These results show that the PFC has a central role in top-down regulation of information processing. Top-down inhibition of crossmodal, task-irrelevant information is stronger when the processing demands in the PFC are high (such as during WM task performance) as compared to conditions in which the processing demands are low such as during rest or during local anesthesia of the PFC. doi:10.1016/j.ijpsycho.2010.06.012
Abstracts / International Journal of Psychophysiology 77 (2010) 206–238
items during encoding of visuospatial locations. A strong targetrelated theta response predicts high visual working memory capacity, whereas a strong response of this theta network to encoding of distracting items predicts low memory capacity. During maintenance of visual items, on the other hand, sustained cross-frequency phase coupling between theta and gamma (50–70 Hz) is obtained at brain areas storing target items. This theta–gamma phase coupling shows a load-dependent increase of up to four items to be retained. When memory load is further increased, theta and gamma phases are decoupled again. The magnitude of memory load-dependent theta– gamma phase coupling predicts individual working memory capacity. Efficient suppression of distracter items during a retention period, however, is reflected by increased EEG alpha (8–12 Hz) amplitude at brain areas processing distracting visual information. Memory capacity can also be predicted by alpha amplitude, in this case, based on the efficient inhibition of distracter maintenance. Moreover, by entraining alpha activity using repetitive TMS, it can be shown that memory capacity is increased as the neural mechanism of distracter suppression is reinforced by the stimulation. doi:10.1016/j.ijpsycho.2010.06.010
Frequency-selective generators of oscillatory brain activity allow identifying processes of a working memory Nina N. Danilovaa, Elena A. Strabykinab a Department of Psychology, Lomonosov Moscow State University, Russia b Department of Computational Mathematics and Cybernetics, Lomonosov Moscow State University, Russia The aim of this study to investigate processes of visual working memory by a new method of micro structural analysis of event-related oscillations based on the pacemaker hypothesis of rhythm genesis (Danilova, 2006, 2008). Computation of equivalent current dipoles based on multichannel EEG data and their superposition onto slices of structural MRI for an individual human brain was used to identify localization of activated frequency-selective gamma (30-75 Hz), beta (14-29 Hz) and theta (4-7 Hz) generators. In experiments with working memory (10 participants), the subject has to memorize four pairs of two-digit numbers that are visually-presented and retain them during a delay interval for the subsequent comparison with target and no-target stimuli and performing motor reaction on target stimuli. The similarity of activated brain structures was found for the perception stage and retention interval. High-frequency generators were localized in frontal, associative (temporal, parietal) cortex, visual cortex, and cerebellum. Activity level in the frontal area during the perception and number memorization was higher than during the retention interval. However, during the delay period, the maximum activity of highfrequency generators was shifting from a frontal to an associative cortex and the cerebellum. The growth of cerebellum activity and the activation of visual cortex may be attributed to a motor readiness, the ability to predict the moment of stimulus presentation, and activating sensory memory traces. The investigation of the dynamic of memory retention showed that frequency-selective gamma and beta generators operating at different frequencies form bursts of join activity which periodically appears and disappears. The join activity of the frontal brain area with the visual and temporal cortex occurs during the delay interval and is absent at the perception stages. This suggests that during the retention interval, there is the interaction of local neuron networks represented by activated high-frequency generators. It facilitates rewriting the numerical information (LT-memory traces) from associative brain areas into prefrontal cortex, where it assumes an active form for subsequent use in behavior. Because theta rhythm is connected with encoding function, we have investigated the integra-
tion frequency-selective theta generators with high-frequency gamma and beta generators. For this aim, we used weighed centroid method for clusterization of neural sources in the dipole model of the brain. Results supported periodic fluctuations of join activity of gamma, beta, and theta generators. Localization of centroids showed repeated join activity in the prefrontal and/or cingular cortex, temporal, visualparietal cortex, cerebellum and thalamus. Our finding highlights the role of frequency-selective generators in the sub-function of visual working memory – the retention of memory traces in active form for future use in behavior. Research was supported by Russian Humanitarian Scientific Fund project No 10-06 00481а. doi:10.1016/j.ijpsycho.2010.06.011
How the brain handles distraction during working memory processing Synnöve Carlsona,b, Yuanye Mac Brain Research Unit, Low Temperature Laboratory, Aalto University School of Science and Technology, Espoo, Finland b Neuroscience Unit, Institute of Biomedicine/Physiology, University of Helsinki, Finland c Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, China a
Distraction tends to impair working memory (WM) performance, but the underlying neuronal mechanisms are not clear. Here two studies are described in which the role of the prefrontal cortex (PFC) in the handling of distraction was investigated. In the first study, we investigated the effects of visual and auditory distraction on single neuron activity in the monkey PFC. Intracortical microelectrode recordings were conducted in two monkeys (Macaca mulatta) trained to perform visual and auditory spatial delayed-matching-to-sample (DMTS) tasks. Visual or auditory distracters were presented randomly during the delay period of the memory task. Distracters impaired WM task performance and affected the PFC neuronal activity. Distraction that was of the same sensory modality as the memorandum was more likely to impair WM performance and interferes with memory-related neuronal activity than distracters that were of a different sensory modality. The study also shows that neurons that are not involved in memory processing in less demanding conditions may become engaged in WM processing in more demanding conditions, thus suggesting that the PFC has mechanisms that help compensate for disruptive effects of external distracters. In the second study, we recorded auditory evoked potentials (AEPs) to task-irrelevant sounds in the PFC and parietal cortex (PC) of three monkeys (M. mulatta) while they performed a visual DMTS task; taskirrelevant sounds were presented during the WM processing and the intertrial intervals (ITI). The amplitudes of the AEPs in the PFC and PC to task-irrelevant tones were larger during the ITI than during WM processing. AEPs were also recorded in the PC after either a local anesthetic (procaine) or saline was injected intracortically bilaterally in the PFC. AEPs recorded in the PC to the sounds after the procaine injection were larger compared to the AEPs recorded after saline injections. These results show that the PFC has a central role in top-down regulation of information processing. Top-down inhibition of crossmodal, task-irrelevant information is stronger when the processing demands in the PFC are high (such as during WM task performance) as compared to conditions in which the processing demands are low such as during rest or during local anesthesia of the PFC. doi:10.1016/j.ijpsycho.2010.06.012