Middle Temporal Regions Research Articles

Prepulse inhibition and “psychosis-proneness” in healthy individuals: An fMRI study

Objective Prepulse inhibition (PPI) of the startle response provides an operational index of sensorimotor gating that is reliably demonstrable in both human and animal subjects. Patients with schizophrenia, first-degree relatives of patients with schizophrenia, patients with schizotypal personality disorder and healthy individuals scoring high on psychometric measures of psychosis-proneness display reduced PPI. This study examined associations between individual differences in “psychosis-proneness” and brain activity during a tactile prepulse inhibition paradigm previously found to reveal activation in controls and deficient activation in schizophrenia patients in the striatum, thalamus, insula, hippocampal, temporal, inferior frontal, and inferior parietal regions. Methods Fourteen right-handed healthy men underwent psychophysiological testing and functional magnetic resonance imaging (fMRI) during a 15-min tactile PPI paradigm involving the use of tactile stimuli as both the pulse (a 40-ms presentation of 30 psi air-puff) and the prepulse (a 20-ms presentation of 6 psi air-puff presented 30-ms or 120-ms before the pulse). Individual differences in “psychosis-proneness” were assessed with Psychoticism scale of the Eysenck Personality Questionnaire-Revised (EPQ-R). Results High psychosis-proneness was associated with lower PPI and reduced activity in the inferior frontal gyrus, insula extending to putamen and thalamus, parahippocampal gyrus, and inferior parietal and middle temporal regions. No regional activity correlated positively with psychosis-proneness. Conclusions The present observations extend the findings observed previously in people with schizophrenia to people with high psychosis-proneness, providing support to continuum theories of psychosis with implications for understanding trait-related neural deficits in schizophrenia.

Sequential activation of human oculomotor centers during planning of visually-guided eye movements: a combined fMRI-MEG study.

We used magneto-encephalography (MEG) to measure visually evoked activity in healthy volunteers performing saccadic eye movements to visual targets. The neuromagnetic activity was analyzed from regions of cortical activation identified in separate functional magnetic resonance imaging (fMRI) studies. The latency of visual responses significantly increased from the Middle Temporal region (MT+) to the Intraparietal Sulcus (IPS) to the Frontal Eye Field (FEF), and their amplitude was greater in the hemisphere contralateral to the visual target. Trial-to-trial variability of oculomotor reaction times correlated with visual response latency across cortical areas. These results support a feedforward recruitment of oculomotor cortical centers by visual information, and a model in which behavioral variability depends on variability at different neural stages of processing.

Cerebral Differences in Explicit and Implicit Emotional Processing – An fMRI Study

The processing of emotional facial expression is a major part of social communication and understanding. In addition to explicit processing, facial expressions are also processed rapidly and automatically in the absence of explicit awareness. We investigated 12 healthy subjects by presenting them with an implicit and explicit emotional paradigm. The subjects reacted significantly faster in implicit than in explicit trials but did not differ in their error ratio. For the implicit condition increased signals were observed in particular in the thalami, the hippocampi, the frontal inferior gyri and the right middle temporal region. The analysis of the explicit condition showed increased blood-oxygen-level-dependent signals especially in the caudate nucleus, the cingulum and the right prefrontal cortex. The direct comparison of these 2 different processes revealed increased activity for explicit trials in the inferior, superior and middle frontal gyri, the middle cingulum and left parietal regions. Additional signal increases were detected in occipital regions, the cerebellum, and the right angular and lingual gyrus. Our data partially confirm the hypothesis of different neural substrates for the processing of implicit and explicit emotional stimuli.

Categorical and thematic knowledge representation in the brain: Neural correlates of taxonomic and thematic conceptual relations

Most current models of knowledge organization in the brain are based on hierarchical or taxonomic categories (animals, tools). Another important organizational pattern is thematic categorization, i.e. categories held together by external relations, a unifying scene or event (car and garage).We used fMRI to examine neural activation patterns as subjects performed a category construction task where these two category types were contrasted. Subjects were visually presented with a target word followed by the presentation of two match words and had to choose by button press one match that goes best with the target word. In the balanced or cross-categorization condition (Car/Garage Bus) both match words fit the target; in the biased conditions only one match word fit the target either thematically (Car/Garage Brush) or taxonomically (Car/Bus Eraser).We found that in the biased conditions, thematic and taxonomic categories recruited very similar cortical regions: left inferior frontal, middle temporal and occipital regions. In the balanced condition subjects showed no behavioral preference for either thematic or taxonomic matches. However, contrasting signal changes during a subjective taxonomic choice in the presence of a thematic alternative vs. a subjective thematic choice in the presence of a taxonomic alternative required the additional recruitment of right middle frontal gyrus, left precuneus and left thalamus.Our results suggest that thematic relations between objects are processed similarly to taxonomic relations, but require less cerebral processing demand, providing validation for thematic categories as an alternative principle of conceptual organization.

Age-related differences in brain activity underlying identification of emotional expressions in faces

We used fMRI to explore brain activity in young and old adults, while they viewed and labeled faces expressing different emotions as well as neutral expressions. Older adults had significantly greater difficulty identifying expressions of sadness, anger and disgust than young adults. Both groups performed at ceiling for happy expressions. The functional neuroimaging data revealed that both young and old adults recruited a pattern of activity that distinguished happy expressions from all other expressions, but the patterns were age-specific. Older adults showed increased activity in ventromedial prefrontal cortex, lingual gyrus and premotor cortex for happy expressions, whereas younger adults recruited a more widely distributed set of regions including the amgydala, ventromedial prefrontal cortex, lateral prefrontal regions and bilateral inferior parietal and superior temporal areas. Conversely, younger adults showed more activity in the dorsal anterior cingulate for other types of expressions, and older adults had more activity in dorsal cingulate, as well as middle and inferior frontal gyri, somatosensory cortex, insula and middle temporal regions. These results support previous research demonstrating age differences in brain activity during emotional processing, and suggest possible age-related differences in cognitive strategy during identification of happy faces, despite no effect of age on this ability.

Temporally Graded Activation of Neocortical Regions in Response to Memories of Different Ages

The temporally graded memory impairment seen in many neurobehavioral disorders implies different neuroanatomical pathways and/or cognitive mechanisms involved in storage and retrieval of memories of different ages. A dynamic interaction between medial-temporal and neocortical brain regions has been proposed to account for memory's greater permanence with time. Despite considerable debate concerning its time-dependent role in memory retrieval, medial-temporal lobe activity has been well studied. However, the relative participation of neocortical regions in recent and remote memory retrieval has received much less attention. Using functional magnetic resonance imaging, we demonstrate robust, temporally graded signal differences in posterior cingulate, right middle frontal, right fusiform, and left middle temporal regions in healthy older adults during famous name identification from two disparate time epochs. Importantly, no neocortical regions demonstrated greater response to older than to recent stimuli. Our results suggest a possible role of these neocortical regions in temporally dating items in memory and in establishing and maintaining memory traces throughout the lifespan. Theoretical implications of these findings for the two dominant models of remote memory functioning (Consolidation Theory and Multiple Trace Theory) are discussed.

Competing Neural Responses for Auditory and Visual Decisions

Why is it hard to divide attention between dissimilar activities, such as reading and listening to a conversation? We used functional magnetic resonance imaging (fMRI) to study interference between simple auditory and visual decisions, independently of motor competition. Overlapping activity for auditory and visual tasks performed in isolation was found in lateral prefrontal regions, middle temporal cortex and parietal cortex. When the visual stimulus occurred during the processing of the tone, its activation in prefrontal and middle temporal cortex was suppressed. Additionally, reduced activity was seen in modality-specific visual cortex. These results paralleled impaired awareness of the visual event. Even without competing motor responses, a simple auditory decision interferes with visual processing on different neural levels, including prefrontal cortex, middle temporal cortex and visual regions.

Effects of generation mode in fMRI adaptations of semantic fluency: Paced production and overt speech

Verbal fluency is a widely used neuropsychological paradigm. In fMRI implementations, conventional unpaced (self-paced) versions are suboptimal due to uncontrolled timing of responses, and overt responses carry the risk of motion artifact. We investigated the behavioral and neurofunctional effects of response pacing and overt speech in semantic category-driven word generation. Twelve right-handed adults (8 females), ages 21–37 were scanned in four conditions each: paced-overt, paced-covert, unpaced-overt, and unpaced-covert. There was no significant difference in the number of exemplars generated between overt versions of the paced and unpaced conditions. Imaging results for category-driven word generation overall showed left-hemispheric activation in inferior frontal cortex, premotor cortex, cingulate gyrus, thalamus, and basal ganglia. Direct comparison of generation modes revealed significantly greater activation for the paced compared to unpaced conditions in right superior temporal, bilateral middle frontal, and bilateral anterior cingulate cortex, including regions associated with sustained attention, motor planning, and response inhibition. Covert (compared to overt) conditions showed significantly greater effects in right parietal and anterior cingulate, as well as left middle temporal and superior frontal regions. We conclude that paced overt paradigms are useful adaptations of conventional semantic fluency in fMRI, given their superiority with regard to control over and monitoring of behavioral responses. However, response pacing is associated with additional non-linguistic effects related to response inhibition, motor preparation, and sustained attention.

The role of MT+/V5 during biological motion perception in Asperger Syndrome: An fMRI study

Asperger Syndrome (AS), a condition on the autistic spectrum, is characterized by deficits in the ability to use social cues to infer mental state information. Few studies have examined whether these deficits might be understood in terms of differences in visual information processing. The present study employed functional magnetic resonance imaging to examine differences in brain activity among individuals with AS while performing a task that typically leads to the automatic interpretation of human movement. Despite similar behavioural performance, significantly less activity was found for the AS group (relative to a control group) in inferior, middle and superior temporal regions, including the human analogue of MT+/V5. These data suggest that AS is associated with unique patterns of brain activity during the perception of visually presented social cues.

Semantic and phonological task-set priming and stimulus processing investigated using magnetoencephalography (MEG)

In this study the neural substrates of semantic and phonological task priming and task performance were investigated using single word task-primes. Magnetoencephalography (MEG) data were analysed using Synthetic Aperture Magnetometry (SAM) to determine the spatiotemporal and spectral characteristics of cortical responses. Comparisons were made between the task-prime conditions for evidence of differential effects as a function of the nature of the task being primed, and between the task-prime and the task performance responses for evidence of parallels in activation associated with preparation for and completion of a specific task.Differential priming effects were found. Left middle temporal and inferior frontal voxels showed a statistically significant power decrease associated with the semantic task-prime, and a power increase associated with the phonological task-prime, within beta and gamma frequency bands respectively. Similarities between the task-related differential effects associated with task-prime presentation and those associated with target stimulus presentation were also found. For example, within the semantic task condition, left superior frontal and middle temporal regions showed a significant power decrease within both task-prime and target epochs; within the phonological task condition there were significant parietal and cerebellar power decreases within both types of epoch.In addition there was evidence within the priming epochs of dissociable patterns of activity which could be interpreted as indices of de-activation of task-irrelevant networks. Following a phonological task-prime, significant power increases were observed in those inferior frontal and middle temporal regions in which significant power decreases were associated with semantic task priming and performance.

Imaging brain activity during natural vision using CASL perfusion fMRI

Functional MRI (fMRI) has begun to be used to explore human brain activity during ecological and natural conditions. Arterial spin labeling (ASL) perfusion fMRI provides an appealing approach for imaging sustained brain activity during natural conditions because of its long-term temporal stability and ability to noninvasively quantify absolute cerebral blood flow (CBF). The present study used ASL perfusion fMRI to measure brain activation patterns associated with natural vision by concurrently recording CBF and blood oxygen level-dependent (BOLD) contrasts while subjects were freely viewing a cartoon movie. Reliable quantitative whole-brain CBF values ( approximately 60 mL/100g/min) as well as regional CBF values (45 approximately 80 mL/100g/min) were measured during movie viewing and resting states. The perfusion contrast revealed CBF increases in multiple visual pathway areas and frontal areas, and CBF decreases in ventromedial frontal cortex and superior temporal cortex during movie viewing compared to resting states. Concurrent BOLD contrast revealed similar but weaker activation and deactivation patterns. Regression analyses of both CBF data and BOLD data showed significant associations between activation in the middle temporal (MT) region and subjects' perception of motion. Region of interest analysis based on a priori literature-defined MT demonstrated significant monotonic stepwise associations between the intensity of motion perception and the CBF and BOLD signal changes. These results demonstrate the feasibility of using ASL perfusion fMRI for imaging both sustained and dynamic effects in neural activation during natural and ecologically valid situations, and support the notion of maintained functional segregation and specialization during natural vision.

EEG dipole analysis of motor-priming foreperiod activity reveals separate sources for motor and spatial attention components

Objective This study employed EEG source localisation procedures to study the contribution of motor preparatory and attentional processing to foreperiod activity in an S1–S2 motor priming task. Methods Behavioural and high-density event-related potential (ERP) data were recorded in an S1–S2 priming task where participants responded to S2 with a left or right-hand button press. S1 either provided information about response hand (informative) or ambiguous information (uninformative). Results Responses were significantly faster in informative trials compared with uninformative trials. Dipole source analysis of foreperiod lateralized ERPs revealed sources of motor preparatory activity in the dorsolateral premotor cortex (PMd) in line with previous work. In addition, two spatial attention components (ADAN, LDAP) were identified with generators in the PMd and occipitotemporal visual areas in the middle temporal (MT) region, respectively. Separation of motor-related and attentional PMd source locations was reliable along the rostral–caudal axis. Conclusions The presence of attentional components in a motor priming paradigm supports the premotor theory of attention which suggests a close link between attention and motor preparatory processes. Separation of components in the premotor cortex is in accord with a functional division of PMd into rostral (higher-order processing) and caudal (motor-related processing) areas as suggested by imaging work. Significance A prime for response preparation is a trigger for separate, but closely linked, attention-related activity in premotor areas.

A dedicated neural mechanism for vowel selection: A case of relative vowel deficit sparing the number lexicon

We report the case of an Italian speaker (GBC), with classical Wernicke's aphasia following a vascular lesion in the posterior middle temporal region. GBC exhibited a selective deficit in spoken language production affecting vowels more than consonants. In reading from a newspaper, GBC substituted vowels for other vowels from the Italian inventory at a rate of 7/1 compared to consonants. No effects of frequency or grammatical class were found. Vowel errors could also not be accounted for by morphological or known phonological processes. Production of number words, in contrast, was free from phonological errors. While GBC has intact representations of Italian vowels and consonants, his data argue for a separate selection mechanism for vowels that is dissociable from that used for consonants. This case provides neuropsychological evidence for models of word production that distinguish between the abstract phonological properties of a word (e.g., sequencing of phonemic slots, or “CV skeleton”) and a separate representation for the specific sounds (melody).

Maturation of Speech and Language Functional Neuroanatomy in Pediatric Normal Controls

This study explores the relationship between age and resting-state regional cerebral blood flow (rCBF) in regions associated with higher order language skills using a population of normal children, adolescents, and young adults. rCBF was measured in 33 normal participants between the ages of 7 and 19 years using single photon emission computed tomography. Participants' ages were regressed on rCBF values (normalized to whole-brain CBF) in 2 ways: (a) within anatomically defined, language-related regions of interest (ROIs) including Wernicke's area, Broca's area, angular gyrus, planum temporale, and Heschl's gyrus and (b) within clusters of voxels found to be significantly related to age in voxel-wise analyses. rCBF in all anatomically defined ROIs except Heschl's gyrus declined as a function of age. Additionally, voxel-wise analyses revealed clusters where rCBF declined with age in left inferior parietal, left superior temporal, and right middle temporal regions-areas often implicated in higher order language functions. These data suggest that ongoing maturation (e.g., dendritic pruning) in higher order cognitive areas (e.g., angular gyrus) continues into adolescence, as reflected by declining rCBF, while the primary auditory area (Heschl's gyrus) has become a stable neuronal population by age 7 years.

Dissociating Verbal and Nonverbal Conceptual Processing in the Human Brain

Functional neuroimaging has highlighted a left-hemisphere conceptual system shared by verbal and nonverbal processing despite neuropsychological evidence that the ability to recognize verbal and nonverbal stimuli can doubly dissociate in patients with left- and right-hemisphere lesions, respectively. Previous attempts to control for perceptual differences between verbal and nonverbal stimuli in functional neuroimaging studies may have hidden differences arising at the conceptual level. Here we used a different approach and controlled for perceptual confounds by looking for amodal verbal and nonverbal conceptual activations that are common to both the visual and auditory modalities. In addition to the left-hemisphere conceptual system activated by all meaningful stimuli, we observed the left/right double dissociation in verbal and nonverbal conceptual processing, predicted by neuropsychological studies. Left middle and superior temporal regions were selectively more involved in comprehending words--heard or read--and the right midfusiform and right posterior middle temporal cortex were selectively more involved in making sense of environmental sounds and images. Thus, the neuroanatomical basis of a verbal/nonverbal conceptual processing dissociation is established.

Connectivity among semantic associates: An fMRI study of semantic priming

Semantic priming refers to a reduction in the reaction time to identify or make a judgment about a stimulus that has been immediately preceded by a semantically related word or picture and is thought to result from a partial overlap in the semantic associates of the two words. A semantic priming lexical decision task using spoken words was presented in event-related fMRI and behavioral paradigms. Word pairs varied in terms of semantic relatedness and the connectivity between associates. Thirteen right-handed subjects underwent fMRI imaging and 10 additional subjects were tested in a behavioral version of the semantic priming task. It was hypothesized priming would be greatest, reaction time fastest, and cortical activation reduced the most for related word pairs of high connectivity, followed by related word pairs of low connectivity, and then by unrelated word pairs. Behavioral and fMRI results confirmed these predictions. fMRI activity located primarily in bilateral posterior superior and middle temporal regions showed modulation by connectivity and relatedness. The results suggest that these regions are involved in semantic processing.

Age-related reorganization of encoding networks directly influences subsequent recognition memory

Functional magnetic resonance imaging was used to link performance-related brain activity during two word encoding tasks to subsequent recognition for those words in young and older adults. There were no significant group differences in performance during encoding, but the young subjects performed better than the older at the recognition task. Performance-related brain networks strongly differed between the two groups. In young subjects, there were two networks associated with performance, one related to encoding (mainly involving premotor and parietal brain regions) and the other to recognition (involving middle frontal, and lateral and medial temporal regions), whereas the network for older subjects (including prefrontal, premotor, lateral and medial temporal regions) was associated both with encoding and recognition. Areas in this network strongly overlapped with those supporting recognition in the young subjects (e.g., medial temporal lobe), suggesting that older subjects may have recruited these areas to maintain performance during encoding. However, this reorganization of brain networks appears to have come at the cost of subsequent recognition.

Motion verb sentences activate left posterior middle temporal cortex despite static context

The left posterior middle temporal region, anterior to V5/MT, has been shown to be responsive both to images with implied motion, to simulated motion, and to motion verbs. In this study, we investigated whether sentence context alters the response of the left posterior middle temporal region. 'Fictive motion' sentences are sentences in which an inanimate subject noun, semantically incapable of self movement, is coupled with a motion verb, yielding an apparent semantic contradiction (e.g. 'The path comes into the garden.'). However, this context yields no less activation in the left posterior middle temporal region than sentences in which the motion can be applied to the subject noun. We speculate that the left posterior middle temporal region activity in fictive motion sentences reflects the fact that the hearer applies motion to the depicted scenario by scanning it egocentrically.

Domain-general and Domain-sensitive Prefrontal Mechanisms for Recollecting Events and Detecting Novelty

Recollecting the past and discriminating novel from familiar memoranda depend on poorly understood prefrontal cortical (PFC) mechanisms hypothesized to vary according to memory task (e.g. recollection versus novelty detection) and domain of targeted memories (e.g. perceptual versus conceptual). Using event-related fMRI, we demonstrate that recollecting conceptual or perceptual details surrounding object encounters similarly recruits left frontopolar and posterior PFC compared with detecting novel stimuli, suggesting that a domain-general control network is engaged during contextual remembering. In contrast, left anterior ventrolateral PFC coactivated with a left middle temporal region associated with semantic representation, and right ventrolateral PFC with bilateral occipito-temporal cortices associated with representing object form, depending on whether recollections were conceptual or perceptual. These PFC/posterior cortical dissociations suggest that during recollection, lateralized ventrolateral PFC mechanisms bias posterior conceptual or perceptual feature representations as a function of memory relevance, potentially improving the gain of bottom-up memory signals. Supporting this domain-sensitive biasing hypothesis, novelty detection also recruited right ventrolateral PFC and bilateral occipito-temporal cortices compared with conceptual recollection, suggesting that searching for novel objects heavily relies upon perceptual feature processing. Collectively, these data isolate task- from domain-sensitive PFC control processes strategically recruited in the service of episodic memory.

Reading skills after left anterior temporal lobe resection: an fMRI study

Maintaining language functions after left hemisphere lesions has been associated with compensatory right hemisphere activation. It remains unclear whether recruitment of right hemisphere regions necessarily provides an effective mechanism to compensate for language deficits. To investigate the compensatory mechanisms that mediate good reading skills in patients after left anterior temporal lobe resection for mesial temporal lobe epilepsy (mTLE), we tested for the effect of their reading ability on the regional fMRI (functional MRI) signal elicited by sentence reading. Sixteen control subjects and 16 patients participated in the study. In the activation condition, they silently read nine-word sentences, and in the baseline condition they viewed nine-word sentences after all the letters were transformed into false fonts. Reading ability in controls and patients significantly (P < 0.05, corrected) predicted activations in a left hemisphere middle temporal region that was part of the normal sentence reading system. In addition, reading ability in patients, but not controls, significantly predicted activation in the right inferior frontal sulcus, right hippocampus and right inferior temporal sulcus. Right inferior frontal activation was only observed in the patients. In contrast, right hippocampal and inferior temporal activation was observed in all controls and in patients whose reading ability was within the normal range, indicating the importance of these regions for efficient encoding during normal sentence reading. We conclude that proficient reading skills following left anterior temporal lobe resection for mTLE rely on two mechanisms: (i) integrating regions from the normal system (i.e. the left middle temporal, right hippocampus and anterior superior temporal sulcus); and (ii) recruiting right hemisphere regions (i.e. the right inferior frontal sulcus) that are not activated in control subjects.