Activation in or near the fusiform gyrus was estimated to faces and control stimuli. Activation peaked at 165 ms and was strongest to digitized photographs of human faces, regardless of whether they were presented in color or grayscale, suggesting that face- and color-specific areas are functionally separate. Schematic sketche evoked approximately 30% less activation than did face photographs. Scrambling the locations of facial features reduced the response by approximately 25% in either hemisphere, suggesting that configurational versus analytic processing is not lateralized at this latency. Animal faces evoked approximately 50% less activity, and common objects, animal bodies or sensory controls evoked approximately 80% less activity than human faces. The (small) responses evoked by meaningless control images were stronger when they included surfaces and shading, suggesting that the fusiform gyrus may use these features in constructing its face-specific response. Putative fusiform activation was not significantly related to stimulus repetition, gender or emotional expression. A midline occipital source significantly distinguished between faces and control images as early as 110 ms, but was more sensitive to sensory qualities. This source significantly distinguished happy and sad faces from those with neutral expressions. We conclude that the fusiform gyrus may selectively encode faces at 165 ms, transforming sensory input for further processing.

The planning and execution of movements involve areas of the cerebral cortex that are separated in their activity both temporally and spatially. However, the mechanism by which these areas combine to produce a co-ordinated movement is unknown. Studies of the activity of neurones in the sensorimotor cortex in monkeys and humans have shown synchronous oscillatory activity in the 15-30 Hz range (Murthy & Fetz, 1992, 1996aSanes & Donoghue, 1993;Baker et al. 1997;Donoghue et al. 1998). These synchronous oscillations have been suggested to link the disparate motor signals together in a manner analogous to the perceptual 'binding' of stimulus attributes in the visual cortex (Singer & Gray, 1995), where the observed neuronal synchronization is attributed to neurones that participate in the encoding of related information. Sanes & Donoghue (1993) and Murthy & Fetz (1996a) have shown that oscillations in monkey sensorimotor cortex are synchronous over large distances (up to 14 mm), suggesting the involvement of large neuronal populations. However, Murthy & Fetz (1996b) concluded that the oscillatory episodes had no consistent relationship with a variety of motor tasks, and suggested that rather than being involved directly in 'binding' during movement execution, the oscillations could be a neuronal correlate of attention during sensorimotor tasks. 1. Recent reports have shown task-related changes in oscillatory activity in the 15-30 Hz range in the sensorimotor cortex of human subjects and monkeys during skilled hand movements. In the monkey these oscillations have been shown to be coherent with oscillatory activity in the electromyographic activity of hand and forearm muscles. 2. In this study we investigated the modulation of oscillations in the electromyogram (EMG) of human volunteers during tasks requiring precision grip of two spring-loaded levers. 3. Two tasks were investigated: in the 'hold' task, subjects were required to maintain a steady grip force (ca 2·1 N or 2·6 N) for 8 s. In the 'ramp' task, there was an initial hold period for 3 s (force ca 2·1 N) followed by a linear increase in grip force over a 2 s period. The task ended with a further steady hold for 3 s at the higher force level (ca 2·6 N). 4. Surface EMGs were recorded from five hand and forearm muscles in 12 subjects. The coherence of oscillatory activity was calculated between each muscle pair. Frequencies between 1 and 100 Hz were analysed. 5. Each subject showed a peak in the coherence spectra in the 15-30 Hz bandwidth during the hold task. This coherence was absent during the initial movement of the levers. During the ramp task the coherence in the 15-30 Hz range was also significantly reduced during the movement phase, and significantly increased during the second hold period, relative to the initial hold. 6. There was coherence between the simultaneously recorded magnetoencephalogram (MEG) and EMG during steady grip in the hold task; this coherence disappeared during the initial lever movement. Using a single equivalent current dipole source...

The voice we most often hear is our own, and proper interaction between speaking and hearing is essential for both acquisition and performance of spoken language. Disturbed audiovocal interactions have been implicated in aphasia, stuttering, and schizophrenic voice hallucinations, but paradigms for a noninvasive assessment of auditory self-monitoring of speaking and its possible dysfunctions are rare. Using magnetoencephalograpy we show here that self-uttered syllables transiently activate the speaker's auditory cortex around 100 ms after voice onset. These phasic responses were delayed by 11 ms in the speech-dominant left hemisphere relative to the right, whereas during listening to a replay of the same utterances the response latencies were symmetric. Moreover, the auditory cortices did not react to rare vowel changes interspersed randomly within a series of repetitively spoken vowels, in contrast to regular change-related responses evoked 100-200 ms after replayed rare vowels. Thus, speaking primes the human auditory cortex at a millisecond time scale, dampening and delaying reactions to self-produced "expected" sounds, more prominently in the speech-dominant hemisphere. Such motor-to-sensory priming of early auditory cortex responses during voicing constitutes one element of speech self-monitoring that could be compromised in central speech disorders.

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