Adaptive anterior hippocampal responses to oddball stimuli.

An efficient memory system requires the ability to detect and preferentially encode novel stimuli. Human electrophysiological recordings demonstrate differential hippocampal responses to novel vs. familiar stimuli, as well as to oddball stimuli. Although functional imaging experiments of novelty detection have demonstrated hippocampal activation, oddball-evoked hippocampal activation has not been demonstrated. Here we use event-related functional magnetic resonance imaging (fMRI) to measure hippocampal responses to three types of oddball words: perceptual, semantic, and emotional. We demonstrate left anterior hippocampal sensitivity to all three oddball types, with adaptation of responses across multiple oddball presentations. This adaptive hippocampal oddball response was not modulated by depth of processing, suggesting a high degree of automaticity in the underlying process. However, an interaction with depth of encoding for semantic oddballs was evident in a more lateral left anterior hippocampal region. We conclude that the hippocampal response to oddballs demonstrates a second-order novelty effect, being sensitive to the "novelty of novelty" of oddball stimuli. The data provide support for a more general theory that a function of the anterior hippocampus is to register mismatches between expectation and experience.     

Is two better than one? A cross-modal oddball paradigm reveals greater sensitivity of the P300 to emotional face-voice associations

Objective

Studies exploring neurophysiological correlates of main psychiatric disorders have commonly used event-related potentials (ERP) during a visual or an auditory oddball task. The main results concern modulations of the P3b amplitude and/or latency. The present study aims to increase the clinical sensitivity of these P3b modulations by using a more ecological oddball design, using synchronized pairs of audio-visual emotional stimuli.

Method

Two groups of healthy participants, one composed of controls and the other of students displaying anxious and depressive tendencies completed visual, auditory and audio-visual (cross-modal) oddball tasks, in which they had to detect deviant happy and sad stimuli among neutral ones as quickly as possible. Behavioral performance and P3b ERP data were analyzed.

Results

Subjects displaying anxious and depressive tendencies exhibited lower P3b amplitude than the controls, but only in the cross-modal oddball task.

Conclusions

Although the two groups of subjects differed in their levels of co-morbid anxiety and depression, unimodal visual and auditory oddball tasks did not allow us to detect this difference by P3b amplitude modulations, but the cross-modal task did.

Significance

These results suggest that a cross-modal oddball design should be used in future studies to increase the sensitivity of the P300 amplitude differences between healthy participants and those with clinical symptoms.     

Greater sensitivity of the P300 component to bimodal stimulation in an event-related potentials oddball task

ObjectiveStudies that explore neurophysiological correlates of psychiatric disorders have commonly used event-related potentials during a visual or an auditory oddball task with the main results being changes in the P300 component. In the present study, a bimodal oddball design with synchronized pairs of audio–visual stimuli was used to further improve the clinical sensitivity of the P300.MethodsTwo groups of healthy participants, one consisting of students displaying anxious–depressive tendencies and the other of control students, completed visual, auditory and two kinds of audio–visual oddball task (one using emotional stimuli and the other using geometrical figures and simple sounds), in which they had to detect deviant rare stimuli among more frequently presented standard stimuli as quickly as possible. Behavioral performance and P300 data were analyzed.ResultsThe subjects with anxious and depressive tendencies had lower P300 amplitudes than controls, but only in the bimodal tasks.ConclusionsAlthough the two groups differed in their levels of anxiety and depression, only the bimodal tasks were able to identify these differences.SignificancesThese results suggest that a bimodal oddball design should be used in future studies to increase the sensitivity of P300 differences for differentiating between healthy participants and those with clinical symptoms.     

Functional MRI study of auditory and visual oddball tasks.

To seek neural sources of endogenous event-related potentials, brain activations related to rare target stimuli detection in auditory and visual oddball tasks were imaged using a high temporal resolution functional MRI technique. There were multiple modality specific and modality non-specific activations. Auditory specific activations were seen in the bilateral transverse temporal gyri and posterior superior temporal planes while visual specific activations were seen in the bilateral occipital lobes and their junctions with the temporal lobes. Modality non-specific activations were seen in multiple areas including the bilateral parietal and temporal association areas, bilateral prefrontal cortex, bilateral premotor areas, bilateral supplementary motor areas and anterior cingulate gyrus. Results were consistent with previous intracranial evoked potential recording studies, and supported the multiple generator theory of the endogenous event-related potentials.     

Two P300 generators in the hippocampal formation

The presentation of rare target stimuli results in P300 scalp event‐related potentials (ERPs). Generators of this ERP component were found in various brain areas, indicating that multiple cortical and subcortical areas subserve target detection. One of these structures is the mediotemporal lobe (MTL). In the hippocampus, large negative MTL‐P300 potentials are usually observed, whereas reports concerning the rhinal cortex and subiculum are inconsistent. The aim of the present study was to investigate the topography of the mediotemporal P300. ERPs were recorded in epilepsy patients from multicontact depth electrodes, implanted along the longitudinal axis of MTL. Patients had to respond to rare visual target stimuli by a button press. ERP data from the nonfocal hemisphere of 53 patients were included in the analysis. Target detection resulted in large MTL‐P300 potentials in the hippocampus and subiculum. Their latencies did not differ. The hippocampal P300 amplitude increased linearly from anterior to posterior hippocampal body (HB). In contrast, an inverse gradient with larger mean amplitudes in anterior parts was observed for the subiculum. Our results indicate two separate generators of the MTL‐P300, one in the anterior subiculum and one in the posterior HB. Since latencies did not differ, a parallel activation via the entorhinal cortex might have initiated the simultaneous MTL‐P300. Hippocampus and subiculum are essential parts of the MTL‐memory system. Their function within target detection might be to maintain a template of previous stimuli for a comparison with incoming sensory stimuli. © 2009 Wiley‐Liss, Inc.     

Phonemic manipulation in Japanese: an fMRI study

Phonological awareness is the ability to manipulate abstract phonological representations of language and is crucial to the process of learning to read. The neural substrates underlying this appear to be modality-independent at least in alphabetic languages. Japanese language has different orthographic "kana" system, in which each "kana" character strictly corresponds to a syllable. To investigate the neural substrates underlying phonological manipulation of the Japanese language, functional magnetic resonance imaging (fMRI) was used. Neuroimaging data were obtained from adult healthy volunteers during auditory and visual vowel exchange tasks, identical except for the modality of stimuli presentation: a voice and Japanese "kana" characters. Cerebellar vermis was activated by vowel exchange tasks of both modalities. The posterior parts of the superior temporal sulcus (STS) were active during the auditory tasks, suggesting that phonological representations of auditory stimuli are manipulated in this area. These findings are consistent with the previous studies with alphabetic languages. In contrast, the intraparietal sulci, which has been implicated for visuospatial tasks, was active during the visual tasks. This modality-dependent activation may indicate that the simple orthographic rule of the Japanese allows an alternate visual strategy to conduct the phonological awareness task, bypassing manipulation of phonological representation.     

Task-dependent field potentials in human hippocampal formation

Task-dependent field potentials were recorded from implanted electrodes located in the hippocampus and other medial temporal lobe (MTL) structures of epileptic patients undergoing evaluation for possible surgery. In 2-alternative categorization tasks, low-probability auditory, somatic, and visual stimuli elicited potentials with large amplitudes and sharp spatial gradients having the following characteristic spatial distribution: positive posterior to the hippocampus, negative within the hippocampus, and positive anterior to the hippocampus. The sharp spatial gradients within the MTL suggest that these potentials were locally generated, probably by hippocampal pyramidal cells. The MTL potentials were also reliably elicited by exemplars of semantic categories and by stimulus omissions and were sensitive to the sequence of preceding stimuli. However, they were not elicited by the same stimulus sequences when the patient's attention was directed elsewhere and categorization was not required. These results indicate that the MTL potentials reflect endogenous as opposed to obligatory processes. The time course and task dependence of the MTL potentials suggest that MTL structures could contribute to P300 and related event-related potentials on the scalp.     

Behavioral and ERP evidence for amodal sluggish attentional shifting in developmental dyslexia

The goal of this study was to examine the claim that amodal deficits in attentional shifting may be the source of reading acquisition disorders in phonological developmental dyslexia (sluggish attentional shifting, SAS, theory, Hari & Renvall, 2001). We investigated automatic attentional shifting in the auditory and visual modalities in 13 dyslexic young adults with a phonological awareness deficit and 13 control participants, matched for cognitive abilities, using both behavioral and ERP measures. We tested automatic attentional shifting using a stream segregation task (perception of rapid succession of visual and auditory stimuli as one or two streams). Results of Experiment 1(behavioral) suggested that in order to process two successive stimuli separately dyslexic participants required a significantly longer inter-stimulus interval than controls regardless of sensory modality. In Experiment 2 (ERPs), the same participants were tested by means of an auditory and a visual oddball tasks involving variations in the tempo of the same alternating stimuli as Experiment 1. P3b amplitudes elicited by deviant tempos were differently modulated between groups, supporting predictions made on the basis of observations in Experiment 1. Overall, these results support the hypothesis that SAS in dyslexic participants might be responsible for their atypical perception of rapid sequential stimulus sequences in both the auditory and the visual modalities. Furthermore, these results bring new evidence supporting the link between amodal SAS and the phonological impairment in developmental dyslexia.     

Role of the anterior insular cortex in integrative causal signaling during multisensory auditory–visual attention

Coordinated attention to information from multiple senses is fundamental to our ability to respond to salient environmental events, yet little is known about brain network mechanisms that guide integration of information from multiple senses. Here we investigate dynamic causal mechanisms underlying multisensory auditory–visual attention, focusing on a network of right‐hemisphere frontal–cingulate–parietal regions implicated in a wide range of tasks involving attention and cognitive control. Participants performed three ‘oddball’ attention tasks involving auditory, visual and multisensory auditory–visual stimuli during fMRI scanning. We found that the right anterior insula (rAI) demonstrated the most significant causal influences on all other frontal–cingulate–parietal regions, serving as a major causal control hub during multisensory attention. Crucially, we then tested two competing models of the role of the rAI in multisensory attention: an ‘integrated’ signaling model in which the rAI generates a common multisensory control signal associated with simultaneous attention to auditory and visual oddball stimuli versus a ‘segregated’ signaling model in which the rAI generates two segregated and independent signals in each sensory modality. We found strong support for the integrated, rather than the segregated, signaling model. Furthermore, the strength of the integrated control signal from the rAI was most pronounced on the dorsal anterior cingulate and posterior parietal cortices, two key nodes of saliency and central executive networks respectively. These results were preserved with the addition of a superior temporal sulcus region involved in multisensory processing. Our study provides new insights into the dynamic causal mechanisms by which the AI facilitates multisensory attention.     

Hippocampal hemispheric and long‐axis differentiation of stimulus content during episodic memory encoding and retrieval: An activation likelihood estimation meta‐analysis

While there is ample evidence that the hippocampus is functionally heterogeneous along its longitudinal axis, there is still no consensus regarding its exact organization. Whereas spatial memory tasks frequently engage the posterior hippocampus, the regions engaged during episodic memory are more varying and may depend on the specific nature of the stimuli. Here, we investigate the effect of stimulus content on the location of hippocampal recruitment during episodic memory encoding and retrieval of pictorial and verbal material with a meta‐analysis approach, using activation likelihood estimation and restricting the analysis to the hippocampus. Verbal material was associated with left‐lateralized anterior activation, compared to pictorial material that recruited a more posterior aspect of the hippocampus, primarily within the right hemisphere. This effect held for encoding of both single items and item–item associations but was less clear during retrieval. The findings lend further support to a functional subdivision of the hippocampus along its longitudinal axis and indicate that the content of episodic memories is one factor that determines the location of hippocampal recruitment. © 2015 Wiley Periodicals, Inc.     

Cognitive functions of the temporal lobe in the dog: a review

1 The current paper reviews the role of temporal lobe structures in learning and different kinds of memory, with an emphasis on behavioral tasks that re auditory stimuli. 2 The effects of lesions to structures in the temporal lobe were examined in separate groups of dogs, which were trained on an auditory spatial delayed response, or in a trial-unique auditory delayed match to sample recognition task. 3 Spatial memory was impaired after bilateral hippocampal lesions. On the other hand, neither an anterior temporal lesion or rhinal cortical injury nor combined lesion to the hippocampus and the anterior temporal lobe, affected postoperative retraining and performance of the spatial task. 4 Auditory recognition memory task was not impaired after a hippocampal and/or rhinal cortex lesion. However, postoperative retraining of the task was impaired after a lesion to auditory association areas. 5 These results confirm the role of the hippocampus in spatial memory in the dog. On the other hand, the organization of auditory recognition functions within the temporal lobe appears to be different from those described for visual recognition functions.     

From details to large scale: The representation of environmental positions follows a granularity gradient along the human hippocampal and entorhinal anterior–posterior axis

In rodents representations of environmental positions follow a granularity gradient along the hippocampal and entorhinal anterior–posterior axis; with fine‐grained representations most posteriorly. To investigate if such a gradient exists in humans, functional magnetic resonance imaging data were acquired during virtual environmental learning of the objects' positions and the association between the objects and room geometry. The Objects‐room geometry binding led to increased activation throughout the hippocampus and in the posterior entorhinal cortex. Within subject comparisons related specifically to the level of spatial granularity of the object position encoding showed that activation in the posterior and intermediate hippocampus was highest for fine‐grained and medium‐grained representations, respectively. In addition, the level of fine granularity in the objects' positions encoded between subjects correlated with posterior hippocampal activation. For the anterior hippocampus increased activation was observed for coarse‐grained representations as compared to failed encoding. Activation in anterior hippocampus correlated with the number of environments in which the objects positions were remembered when permitting a coarse representation of positions. In the entorhinal cortex, activation in the posterior part correlated with level of fine granularity for the objects' positions encoded between subjects, and activation in the posterior and intermediate entorhinal cortex increased for medium‐grained representations. This demonstrates directly that positional granularity is represented in a graded manner along the anterior–posterior axis of the human hippocampus, and to some extent entorhinal cortex, with most fine‐grained positional representations posteriorly. © 2014 Wiley Periodicals, Inc.     

Effects of attention on dichotic listening: an 15O-PET study

The present study investigated the effect of attention on brain activation in a dichotic listening situation. Dichotic listening is a technique to study laterality effects in the auditory sensory modality. Two different stimuli were presented simultaneously, one in each ear. Twelve subjects listened to lists of consonant-vowel syllables, or short musical instrument passages, with the task of detecting a "target" syllable or musical instrument by pressing a button. The target stimulus appeared an equal number of times in the left and right ear. The subjects were instructed to either concentrate on the stimuli presented in both ears, or only on the left or right ear stimulus. Brain activation was measured with 15O-PET, and significant changes in regional normalized counts (rNC) were evaluated using statistical parametric mapping (SPM96) software. Concentrating on either the right or left ear stimulus significantly decreased activity bilaterally in the temporal lobes compared to concentrating on both ear stimuli, at the expense of an increased activation in the right posterior and inferior superior parietal lobe. The CV-syllables activated areas corresponding to the classic language areas of Broca and Wernicke. The musical instrument stimuli mainly activated areas in visual association cortex, cerebellum, and the hippocampus. An interpretation of the findings is that attention has a facilitating effect for auditory processing, causing reduced activation in the primary auditory cortex when attention is explicitly recruited. The observed activations in the parietal lobe during the focused attention conditions could be part of a modality non-specific "attentional network".     

Involvement of the dorsal and ventral attention networks in oddball stimulus processing: A meta‐analysis

The aim of this study was to provide the first, comprehensive meta‐analysis of the neuroimaging literature regarding greater neural responses to a deviant stimulus in a stream of repeated, standard stimuli, termed here oddball effects. The meta‐analysis of 75 independent studies included a comparison of auditory and visual oddball effects and task‐relevant and task‐irrelevant oddball effects. The results were interpreted with reference to the model in which a large‐scale dorsal frontoparietal network embodies a mechanism for orienting attention to the environment, whereas a large‐scale ventral frontoparietal network supports the detection of salient, environmental changes. The meta‐analysis yielded three main sets of findings. First, ventral network regions were strongly associated with oddball effects and largely common to auditory and visual modalities, indicating a supramodal “alerting” system. Most ventral network components were more strongly associated with task‐relevant than task‐irrelevant oddball effects, indicating a dynamic interplay of stimulus saliency and internal goals in stimulus‐driven engagement of the network. Second, the bilateral inferior frontal junction, an anterior core of the dorsal network, was strongly associated with oddball effects, suggesting a central role in top‐down attentional control. However, other dorsal network regions showed no or only modest association with oddball effects, likely reflecting active engagement during both oddball and standard stimulus processing. Finally, prominent oddball effects outside the two networks included the sensory cortex regions, likely reflecting attentive and preattentive modulation of early sensory activity, and subcortical regions involving the putamen, thalamus, and other areas, likely reflecting subcortical involvement in alerting responses. Hum Brain Mapp 35:2265–2284, 2014. © 2013 Wiley Periodicals, Inc .     

The effect of visual task difficulty and attentional direction on the detection of acoustic change as indexed by the Mismatch Negativity

Näätänen's model of auditory processing purports that attention does not affect the MMN. The present study investigates this claim through two different manipulations. First, the effect of visual task difficulty on the passively elicited MMN is assessed. Second, the MMNs elicited by stimuli under attended and ignored conditions are compared. In Experiment 1, subjects were presented with mixed sequences of equiprobable auditory and visual stimuli. The auditory stimuli consisted of standard (80 dB SPL 1000 Hz), frequency deviant (1050 Hz), and intensity deviant (70 dB SPL) tone pips. In a first instance, subjects were instructed to ignore the auditory stimulation and engage in an easy and difficult visual discrimination task (focused condition). Subsequently, they were asked to attend to both modalities and detect visual and auditory deviant stimuli (divided condition). The results indicate that the passively elicited MMN to frequency and intensity deviants did not significantly vary with visual task difficulty, in spite of the fact that the easy and difficult tasks showed a wide variation in performance. The manipulation of the attentional direction (focused vs. divided conditions) did result in a significant effect on the MMN elicited by the intensity, but not frequency, deviant. The intensity MMN was larger at frontal sites when subjects' attention was directed to both modalities as compared to only the visual modality. The attentional effect on the MMN to the intensity deviants only may be due to the specific deviant feature or the poorer perceptual discriminability of this deviant from the standard. Experiment 2 was designed to address this issue. The methods of Experiment 2 were identical to those of Experiment 1 with the exception that the intensity deviant (60 dB SPL) was made to be more perceptible than the frequency deviant (1016 Hz) when compared to the standard stimulus (80 dB SPL 1000 Hz). The results of Experiment 2 also demonstrated that the passively elicited MMN was not affected by large variations in visual task difficulty; this provides convincing evidence that the MMN is independent of visual task demands. Similarly to Experiment 1, the direction of attention again had a significant effect on the MMN. In Experiment 2, however, the frequency MMN (and not the intensity MMN) was larger at frontal sites during divided attention compared to focused visual attention. The most parsimonious explanation of these results is that attention enhances the discriminability of the deviant from the standard background stimulation. As such, small acoustic changes would benefit from attention whereas the discriminability of larger changes may not be significantly enhanced.     

Development of brain mechanisms for processing orthographic and phonologic representations

Developmental differences in the neurocognitive networks for lexical processing were examined in 15 adults and 15 children (9- to 12-year-olds) using functional magnetic resonance imaging (fMRI). The lexical tasks involved spelling and rhyming judgments in either the visual or auditory modality. These lexical tasks were compared with nonlinguistic control tasks involving judgments of line patterns or tone sequences. The first main finding was that adults showed greater activation than children during the cross-modal lexical tasks in a region proposed to be involved in mapping between orthographic and phonologic representations. The visual rhyming task, which required conversion from orthography to phonology, produced greater activation for adults in the angular gyrus. The auditory spelling task, which required the conversion from phonology to orthography, also produced greater activation for adults in the angular gyrus. The greater activation for adults suggests they may have a more elaborated posterior heteromodal system for mapping between representational systems. The second main finding was that adults showed greater activation than children during the intra-modal lexical tasks in the angular gyrus. The visual spelling and auditory rhyming did not require conversion between orthography and phonology for correct performance but the adults showed greater activation in a system implicated for this mapping. The greater activation for adults suggests that they have more interactive convergence between representational systems during lexical processing.     

Visual temporal window of integration as revealed by the visual mismatch negativity event-related potential to stimulus omissions

We studied whether, similarly to the auditory modality, short-period temporal integration processes occur in vision. Event-related potentials (ERP) were recorded for occasional stimulus omissions from sequences of patterned visual stimuli. A posterior negative component emerged only when the constant stimulus onset asynchrony (SOA) was shorter than 150 ms. This upper limit is comparable with the duration of the temporal window of integration observed in the auditory modality (including experiments studying the effects of stimulus omissions). Parameters of the posterior negativity were highly similar irrespective of whether the stimuli were task-relevant or not (Experiment 1). Thus, we identified this potential as the visual mismatch negativity (vMMN) component, which reflects task-independent detection of violating regularities of the stimulation. vMMN was followed by an anterior positivity (the P3a), indicating attentional shifts induced by the stimulus omissions. In Experiment 2, a posterior negativity similar to that observed in Experiment 1 emerged after the termination of short trains of stimuli, again only when the SOA was shorter than 150 ms. These results support the notion of a temporal integration window in the visual modality, the duration of which is between 150 and 180 ms.     

Age-related vulnerabilities along the hippocampal longitudinal axis

Evidence for an anterior-posterior gradient of age-related volume reduction along the hippocampal longitudinal axis has been reported in normal aging, but functional changes have yet to be systematically investigated. The current study applied an advanced brain mapping technique, large deformation diffeomorphic metric mapping (LDDMM), automatically delineating the hippocampus into the anterior and posterior segments based on anatomical landmarks. We studied this anterior-posterior gradient in terms of structural and functional MRI in 66 participants aged from 19 to 79 years. The results showed age-related structural volume reduction in both anterior and posterior hippocampi, with greater tendency for anterior decrease. FMRI task contrasts that robustly activated the anterior (associative/relational processing) and posterior (novelty) hippocampus independently, showed only significant reduction of activation in the anterior hippocampus as age increased. Our results revealed positive correlation between structural atrophy and functional decrease in the anterior hippocampi, regardless of task performance in normal aging. These findings suggest that anatomy and functions related to the anterior hippocampus may be more vulnerable to aging, than previously thought.     

Automatic detection of violations of statistical regularities in the periphery is affected by the focus of spatial attention: A visual mismatch negativity study

We investigated the effect of spatial attention on an event‐related potential signature of automatic detection of violations of statistical regularities, namely, the visual mismatch negativity (vMMN). To vary the task‐field and the location of vMMN‐related stimulation, in the attentional field the stimuli of a tracking task with a steady and a moving (target) bar were presented. The target stimuli of the task appeared either relatively close or far from a passive (task‐irrelevant) oddball or equiprobable sequence at the lower part of the screen. Stimuli of the oddball sequence were shapes tilted either 45° (standard, p = 0.8) or 135° (deviant, p = 0.2), while the equiprobable sequence consisted of additional three shapes with identical number of lines to the oddball stimuli. Deviant stimuli in close proximity to a continuously attended field elicited larger vMMN than similar stimuli farther away from the stimulus field. In the condition with a smaller distance between the field of the tracking task and the vMMN‐related field, the deviant stimuli and the vMMN was followed by a posterior positivity. According to these results, spatial attention modulates vMMN and is capable of initiating further processing of the deviant stimuli.     

Intermodal selective attention. I. Effects on event-related potentials to lateralized auditory and visual stimuli.

The effects of intermodal selective attention on event-related brain potentials (ERPs) were examined in 2 experiments. In experiment 1, auditory ERPs were compared (1) when subjects responded to easy and difficult-to-detect target tones in sequences of tone bursts; and (2) when they ignored the same auditory sequences and played a demanding video game. In experiment 2, auditory ERPs to tone bursts and visual ERPs to vertical line gratings were compared as subjects responded to difficult-to-detect targets in one modality or the other. Attention to auditory stimuli resulted in biphasic enhancements in auditory ERPs, the Nda (negative auditory difference wave, latency 120-160 msec) and the Pda (positive auditory difference wave, latency 200-240 msec) waves. These had longer latencies and somewhat different scalp distributions than N1 and P2 components evoked by non-attended tones. The Nda and Pda could be contrasted with the monophasic processing negativities typically found in dichotic selective attention tasks. Nda amplitudes were larger for difficult-to-detect targets (closely resembling standards) than for standards themselves, but no Ndas were recorded to highly deviant targets. Deviant auditory stimuli evoked mismatch negativities (MMNs) that persisted during visual attention. MMN amplitudes to difficult-to-detect deviants were enlarged with attention, but no change was found in MMN amplitudes to easy-to-detect deviants. In experiment 2 intermodal attention was associated with biphasic changes in visual ERPs over the posterior scalp: the occipital Pdv (100-130 msec), and contralateral-temporal Ndv (120-320 msec) deflections. Deviant visual stimuli also elicited mismatch negativity/N2b components, largest over the inferotemporal cortex contralateral to the stimulated visual field. Like the auditory MMN, the MMN increased in amplitude with attention, but it was also evident during attend auditory conditions. The results suggest that sustained, intermodal attention depends primarily in processing modulations in modality-specific cortex. We found no evidence of the participation of modality non-specific cortex. This excludes the possibility that intermodal attention depends on a single, supramodal attention system. The relatively long latency of intermodal effects suggests that they may depend on the reafferent (top down) modulation, and do not index "template matching" operations.