Gamma-Band Responses Reflect Word/Pseudoword Processing (original) (raw)

Behavioral and Brain Sciences, 1999

If the cortex is an associative memory, strongly connected cell assemblies will form when neurons in different cortical areas are frequently active at the same time. The cortical distributions of these assemblies must be a consequence of where in the cortex correlated neuronal activity occurred during learning. An assembly can be considered a functional unit exhibiting activity states such as full activation (“ignition”) after appropriate sensory stimulation (possibly related to perception) and continuous reverberation of excitation within the assembly (a putative memory process). This has implications for cortical topographies and activity dynamics of cell assemblies forming during language acquisition, in particular for those representing words. Cortical topographies of assemblies should be related to aspects of the meaning of the words they represent, and physiological signs of cell assembly ignition should be followed by possible indicators of reverberation. The following postul...

2002

white matter morphology, which is otherwise difficult Montreal Neurological Institute due to the lack of clear boundaries between adjacent McGill University white matter subregions. Voxel-based morphometry has Montreal, Quebec been used by other investigators to demonstrate norma-Canada H3A 2B4 tive brain asymmetries (Watkins et al., 2001), maturation of white matter tracts (Paus et al., 1999), structural correlates of arithmetic abilities (Isaacs et al., 2001), and dif-Summary ferences in brain morphology in normal versus clinical groups (Vargha-Khadem et al., 1998; Wright et al., 1995; We examined the relationship between brain anatomy Thompson et al., 2001). and the ability to learn nonnative speech sounds, as We trained 59 healthy individuals to distinguish a phowell as rapidly changing and steady-state nonlinguisnetic contrast not present in their native language: the tic sounds, using voxel-based morphometry in 59 dental and retroflex sounds used in Hindi. Previous funchealthy adults. Faster phonetic learners appeared to tional imaging work on phonetic perception has shown have more white matter in parietal regions, especially the involvement of several temporoparietal regions of in the left hemisphere. The pattern of results was simithe left hemisphere (Dé monet et al., 1994; Zatorre et al., lar for the rapidly changing but not for the steady-state 1992, 1996; Binder et al., 1996, 1997; Petersen et al., nonlinguistic stimuli, suggesting that morphological 1988; Paulesu et al., 1993), the superior temporal gyri correlates of phonetic learning are related to the ability bilaterally (Binder et al., 1994; Mazoyer et al., 1993; Jä nto process rapid temporal variation. Greater asymmecke et al., 1998; Mummery et al., 1999), and left inferior try in the amount of white matter in faster learners frontal regions in and around Broca's area (Zatorre et may be related to greater myelination allowing more al., 1992, 1996; Paulesu et al., 1993; Fiez et al., 1995; efficient neural processing, which is critical for the Burton et al., 2000). We predicted that phonetic learning ability to process certain speech sounds. measures would be correlated with differences in brain morphology in language-related cortical areas. In addi

How do neurons work together? Lessons from auditory cortex

Hearing research, 2011

Recordings of single neurons have yielded great insights into the way acoustic stimuli are represented in auditory cortex. However, any one neuron functions as part of a population whose combined activity underlies cortical information processing. Here we review some results obtained by recording simultaneously from auditory cortical populations and individual morphologically identified neurons, in urethane-anesthetized and unanesthetized passively listening rats. Auditory cortical populations produced structured activity patterns both in response to acoustic stimuli, and spontaneously without sensory input. Population spike time patterns were broadly conserved across multiple sensory stimuli and spontaneous events, exhibiting a generally conserved sequential organization lasting approximately 100 ms. Both spontaneous and evoked events exhibited sparse, spatially localized activity in layer 2/3 pyramidal cells, and densely distributed activity in larger layer 5 pyramidal cells and putative interneurons. Laminar propagation differed however, with spontaneous activity spreading upward from deep layers and slowly across columns, but sensory responses initiating in presumptive thalamorecipient layers, spreading rapidly across columns. In both unanesthetized and urethanized rats, global activity fluctuated between "desynchronized" state characterized by low amplitude, high-frequency local field potentials and a "synchronized" state of larger, lower-frequency waves. Computational studies suggested that responses could be predicted by a simple dynamical system model fitted to the spontaneous activity immediately preceding stimulus presentation. Fitting this model to the data yielded a nonlinear selfexciting system model in synchronized states and an approximately linear system in desynchronized states. We comment on the significance of these results for auditory cortical processing of acoustic and non-acoustic information.

Independent and Redundant Information in Nearby Cortical Neurons

Science, 2001

In the primary visual cortex (V1), nearby neurons are tuned to similar stimulus features, and, depending on the manner and time scale over which neuronal signals are analyzed, the resulting redundancy may mitigate deleterious effects of response variability. We estimated information rates in the short-time scale responses of clusters of up to six simultaneously recorded nearby neurons in monkey V1. Responses were almost independent if we kept track of which neuron fired each spike but were redundant if we summed responses over the cluster. Redundancy was independent of cluster size. Summing neuronal responses to reduce variability discards potentially useful information, and the discarded information increases with cluster size.

2001

level system that appears to require attention (Cavanagh, 1992; Lu and Sperling 1996). Evidence of two separate motion systems was first presented by , and modern research (e.g., continues to confirm this notion. Recent studies have shown that this attention based mechanism is Harvard University limited in both spatial and temporal resolution (Lu and Cambridge, Massachusetts 02138 ). In contrast, low-level Beth Israel Deaconess Medical Center mechanisms can signal motion even when a stimulus is Boston, Massachusetts 02215 not attentively tracked and responds to motion at much 3 Department of Neurology higher temporal frequencies. This low-level passive sys-Harvard Medical School and tem is putatively mediated by directionally selective Massachusetts General Hospital cells in the early visual cortices (Hubel and Wiesel, 1968) Boston, Massachusetts 02114 and is velocity based, whereas the high-level system is 4 INSERM position based and depends on attention Cavanagh, 1998, 1999). Since parietal lesions are asso-Lyon, France ciated with deficits in attention, we hypothesized that parietal lesions ought to impair high-level motion perception. In the present report, we examine two high-Summary level motion tasks, namely multiple object tracking and apparent motion. Similarities and differences in the im-Patients with right parietal damage demonstrate a vapairments for these two high-level motion tasks should riety of attentional deficits in their left visual field conreveal similarities and differences in the attention mechtralateral to their lesion. We now report that patients anisms they may call on. with right lesions also show a severe loss in the per-Selective attention mechanisms were tested with a ception of apparent motion in their "good" right visual task of divided attention in which the subject had to field ipsilateral to their lesion. Three tests of attention report a letter presented among three different letters were conducted, and losses were found only in the for 66 or 300 ms. At the offset of the display, the subject contralesional fields for a selective attention and a was required to identify a letter based on its position in multiple object tracking task. Losses in apparent mothe letter string. The cued report for brief visual displays tion, however, were bilateral in all cases. The deficit was first developed by Sperling (1960), and we used a in apparent motion in the parietal patients supports modified version of his task. Recent studies have shown previous claims that this relatively effortless percept how patients with parietal lobe lesions can be affected is mediated by attention. However, the bilateral deficit in their ability to perform this type of task (Duncan et suggests that the disruption is due to a bilateral loss in al., 1999). In contrast to the tasks of Duncan et al., we the temporal resolution of attention to transient events asked our subjects to report only one letter among four, that drive the apparent motion percept. and the subject never knew which letter until briefly after the letters were presented. With only four items, normal

Collectivity in the Brain Sensory Response

1999

A question of cooperative effects in auditory brain processing on various spaceand timescales is addressed. The experimental part of our study is based on Multichannel Magnetoencephalography recordings in normal human subjects. Left, right and binaural stimulations were used, in separate runs, for each subject. The resulting time-series representing left and right auditory cortex activity provide a clear evidence for two levels of neuronal cooperation. One is the local hemispheric collective response, termed M100 for its maximum at around 100ms after a stimulus onset. Its only global characteristics turn out to be time-locked to a stimulus, however, which means that the detailed neuronal evolution is largely stochastic. This, together with the 1/f character of the corresponding power spectrum indicates self-organized criticality as an underlying mechanism. The second level is communication between the two hemispheres with clear laterality effects: as a rule, the contralateral hemisphere leads by ∼10ms. Mutual information analysis points to a direct information transport as a way of this communication.

Gamma-Band Responses Reflect Word/Pseudoword Processing (original) (raw)

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