Bilateral Inferior Parietal Cortex Research Articles

Implicit and explicit processing of kanji and kana words and non-words studied with fMRI

Using functional magnetic resonance imaging (fMRI), we investigated the implicit language processing of kanji and kana words (i.e., hiragana transcriptions of normally written kanji words) and non-words. Twelve right-handed native Japanese speakers performed size judgments for character stimuli (implicit language task for linguistic stimuli), size judgments for scrambled-character stimuli (implicit language task for non-linguistic stimuli), and lexical decisions (explicit language task). The size judgments for scrambled-kanji stimuli and scrambled-kana stimuli produced activations on the bilateral lingual gyri (BA 18), the bilateral occipitotemporal regions (BA 19/37), and the bilateral superior and inferior parietal cortices (BA 7/40). Interestingly, besides these areas, activations of the left inferior frontal region (Broca's area, BA 44/45) and the left posterior inferior temporal cortex (PITC, BA 37), which have been considered as language areas, were additionally activated during size judgment for kanji character stimuli. Size judgment for kana character stimuli also activated Broca's area, the left PITC, and the left supramarginal gyrus (SMG, BA 40). The activations of these language areas were replicated in the lexical decisions for both kanji and kana. These findings suggest that language processing of both kanji and kana scripts is obligatory to literate Japanese subjects. Moreover, comparison between the scrambled kanji and the scrambled kana showed no activation in the language areas, while greater activation in the bilateral fusiform gyri (left-side predominant) was found in kanji vs. kana comparison during the size judgment and the lexical decision. Kana minus kanji activated the left SMG during the size judgment, and Broca's area and the left middle/superior temporal junction during the lexical decision. These results probably reflect that in implicit or explicit reading of kanji words and kana words (i.e., hiragana transcriptions of kanji words), although using largely overlapping cortical regions, there are still some differences. Kanji reading may involve more heavily visual orthographic retrieval and lexical-semantic system through the ventral route, while kana transcriptions of kanji words require phonological recoding to gain semantic access through the dorsal route.

Cortical motor activation in akinetic schizophrenic patients: a pilot functional MRI study.

Akinesia is associated with supplementary motor area (SMA) dysfunction in Parkinson's disease. We looked for a similar association in patients with schizophrenia. Using functional magnetic resonance imaging (fMRI), we compared motor activation in 6 akinetic neuroleptic-treated schizophrenic patients and 6 normal subjects. Schizophrenic patients had a defective activation in the SMA, left primary sensorimotor cortex, bilateral lateral premotor and inferior parietal cortices, whereas the right primary sensorimotor cortex and a mesial frontal area were hyperactive. SMA was hypoactive in akinetic schizophrenic patients, emphasizing the role of this area in motor slowness. Other abnormal signals likely reflect schizophrenia-related abnormal intracortical connections.

Right inferior prefrontal cortex mediates response inhibition while mesial prefrontal cortex is responsible for error detection

Inhibitory control and error detection are among the highest evolved human self-monitoring functions. Attempts in functional neuroimaging to effectively isolate inhibitory motor control from other cognitive functions have met with limited success. Different brain regions in inferior, mesial, and dorsolateral prefrontal cortices and parietal and temporal lobes have been related to inhibitory control in go/no-go and stop tasks. The widespread activation reflects the fact that the designs used so far have comeasured additional noninhibitory cognitive functions such as selective attention, response competition, decision making, target detection, and inhibition failure. Here we use rapid, mixed trial, event-related functional magnetic resonance imaging to correlate brain activation with an extremely difficult situation of inhibitory control in a challenging stop task that controls for noninhibitory functions. The difficulty of the stop task, requiring withholding of a triggered motor response, was assured by an algorithm that adjusted the task individually so that each subject only succeeded on half of all stop trials, failing on the other half. This design allowed to elegantly separate brain activation related to successful motor response inhibition and to inhibition failure or error detection. Brain activation correlating with successful inhibitory control in 20 healthy volunteers could be isolated in right inferior prefrontal cortex. Failure to inhibit was associated with activation in mesial frontopolar and bilateral inferior parietal cortices, presumably reflecting an attention network for error detection.

A procedure for identifying regions preferentially activated by attention to semantic and phonological relations using functional magnetic resonance imaging

A procedure is introduced for using functional magnetic resonance imaging (fMRI) techniques to identify neural regions associated with attention to semantic and phonological aspects of written words within a single group of subjects. Short lists (16 words/list), consisting of visually-presented semantically-related words ( bed, rest) or rhyming words ( weep, beep) were presented rapidly to subjects, who were asked to attend to the relations among the words. Regions preferentially involved in attention to semantic relations appeared within left anterior/ventral inferior frontal gyrus (IFG, approximate Brodmann Area, BA47), left posterior/dorsal IFG (BA44/45), left superior/middle temporal cortex (BA22/21), left fusiform gyrus (BA37), and right cerebellum. Regions preferentially involved in attention to phonological relations appeared within left inferior frontal cortex (near BA6/44, posterior to the semantic regions within IFG described above) and within bilateral inferior parietal cortex (BA40) and precuneus (BA7). This method is notable in that a comparison of the two tasks within some of the individual subjects revealed activation patterns similar to the group average, especially within left inferior frontal and left superior/middle parietal cortices. This fact combined with the efficiency with which the data can be obtained (here, in about an hour of functional scanning) and the adaptability of the task for many different subject populations suggests a wide range of possibilities for this technique: it could be used to track language development (e.g. in children), compare language organization across subject populations (e.g. for dyslexic or blind subjects), and identify language regions within individuals (e.g. potentially to aid in surgical planning).

Bilateral parieto-frontal network for verbal working memory: an interference approach using repetitive transcranial magnetic stimulation (rTMS).

Verbal working memory has been attributed to a left-dominant neuronal network, including parietal, temporal and prefrontal cortical areas. The current study was designed to evaluate the contribution of these brain regions to verbal working memory processes and to assess possible hemispheric asymmetry. The effect of repetitive transcranial stimulation (rTMS) on performance in a verbal working memory task both during, and after an rTMS train (110% of individual motor threshold, 4 Hz) over nine different scalp locations was studied [bilateral middle frontal gyrus (MFG), bilateral supramarginal gyrus (SMG), bilateral inferior parietal cortex (IP) and three different midline control sites]. Significant performance deterioration was observed during rTMS over the left and right MFG and left and right IP. There was no consistent interference effect across subjects over the left or right SMG and the three different midline control sites. The interference effect with the given stimulation parameters did not last beyond the rTMS train itself. The data provide evidence for a symmetrical, bilateral parieto-frontal verbal working memory network. The data are discussed with respect to the competing ideas of a parieto-frontal central executive network vs. a network that processes the inherent semantic and object features of the visually presented verbal stimuli in parallel.

Switching between the Forest and the Trees: Brain Systems Involved in Local/Global Changed-Level Judgments

Visual targets can be coded, in relative terms, at either the local or the global level of stimuli. Previous studies have indicated that targets are identified more slowly when they appear at a new hierarchical level, compared to when they reappear at the same level as in the previous trial. In the present study, we used measures of reaction time and event-related fMRI to investigate factors affecting this switch cost. In particular, we examined the effects of the number of repeated-level trials preceding a switch and whether the cue to switch was either externally or internally mediated. At the behavioral level we found that (1) the time taken to identify a target on a changed-level trial is longer following four repeated-level trials compared to two repeated-level trials, but that runs of six do not produce additional costs over four, and (2) targets can be identified faster following externally cued switches compared to internally mediated switches. We then show that these behavioral effects are associated with distinct patterns of neural activation. Switches performed after two repeated-level trials preferentially activated the precuneus, while those performed after both four and six activated bilateral inferior parietal cortex and motor hand area. Relative to external switches, internal switches activated the putamen, while both kinds of switch conjointly activated the large-scale network proposed to underlie internal/external switches in nonhierarchical tasks. Our data further clarify the mechanisms mediating hierarchical selection.

The calculating brain: an fMRI study

To explore brain areas involved in basic numerical computation, functional magnetic imaging (fMRI) scanning was performed on college students during performance of three tasks; simple arithmetic, numerical magnitude judgment, and a perceptual-motor control task. For the arithmetic relative to the other tasks, results for all eight subjects revealed bilateral activation in Brodmann’s area 44, in dorsolateral prefrontal cortex (areas 9 and 10), in inferior and superior parietal areas, and in lingual and fusiform gyri. Activation was stronger on the left for all subjects, but only at Brodmann’s area 44 and the parietal cortices. No activation was observed in the arithmetic task in several other areas previously implicated for arithmetic, including the angular and supramarginal gyri and the basal ganglia. In fact, angular and supramarginal gyri were significantly deactivated by the verification task relative to both the magnitude judgment and control tasks for every subject. Areas activated by the magnitude task relative to the control were more variable, but in five subjects included bilateral inferior parietal cortex. These results confirm some existing hypotheses regarding the neural basis of numerical processes, invite revision of others, and suggest productive lines for future investigation.

Evolution of functional reorganization in hemiplegic stroke: a serial positron emission tomographic activation study.

We used serial positron emission tomography (PET) to study the evolution of functional brain activity within 12 weeks after a first subcortical stroke. Six hemiplegic stroke patients and three normal subjects were scanned twice (PET 1 and PET 2) by using passive elbow movements as an activation paradigm. Increases of regional cerebral blood flow comparing passive movements and rest and differences of regional cerebral blood flow between PET 1 and PET 2 in patients and normal subjects were assessed by using statistical parametric mapping. In controls, activation was found in the contralateral sensorimotor cortex, supplementary motor area, and bilaterally in the inferior parietal cortex with no differences between PET 1 and PET 2. In stroke patients, at PET 1, activation was observed in the bilateral inferior parietal cortex, contralateral sensorimotor cortex, and ipsilateral dorsolateral prefrontal cortex, supplementary motor area, and cingulate cortex. At PET 2, significant increases of regional cerebral blood flow were found in the contralateral sensorimotor cortex and bilateral inferior parietal cortex. A region that was activated at PET 2 only was found in the ipsilateral premotor area. Recovery from hemiplegia is accompanied by changes of brain activation in sensory and motor systems. These alterations of cerebral activity may be critical for the restoration of motor function.

A Developmental Functional MRI Study of Spatial Working Memory

Functional magnetic resonance imaging (fMRI) was used to examine patterns of cortical activity in children during performance of a spatial working memory task. Six children (8–10 years) and six adults (19–26 years) searched a linear array of four boxes for the appearance of a dot. In the visual blocks, participants made no response. In the motor blocks, participants were instructed to indicate the location of the dot on each trial using a button-press response. In the working memory blocks, participants were instructed to indicate at which location the dot had appeared 1 or 2 trials previously. Both children and adults showed activity in the left precentral and postcentral gyri, as well as the right cerebellum for the motor condition as compared to the visual condition. Comparison of the memory and motor conditions revealed reliable activity in the right superior frontal gyrus (BA 8), right dorsolateral prefrontal cortex (BA 10/46), right superior parietal cortex, and bilateral inferior parietal cortex for both adults and children. These results suggest that spatial working memory tasks activate very similar cortical regions for school-age children and adults. The findings differ from previous imaging studies of nonspatial working memory tasks in that the prefrontal activations observed in the current work tend to be more dorsal. Results are discussed in light of the significant behavioral performance differences observed between child and adult participants.

Direct Comparison of Episodic Encoding and Retrieval of Words: An Event-related fMRI Study

Functional magnetic resonance imaging (fMRI) was used to compare directly episodic encoding and retrieval. During encoding, subjects studied visually presented words and reported via keypress whether each word represented a pleasant or unpleasant concept (intentional, deep encoding). During the retrieval phase, subjects indicated (via keypress) whether visually presented words had previously been studied. No reliable differences were found during the recognition phase for words that had been previously studied and those that had not been studied. Areas preferentially active during encoding (relative to retrieval) included left superior frontal cortex, medial frontal cortex, left superior temporal cortex, posterior cingulate, left parahippocampal gyrus, and left inferior frontal gyrus. Regions more active in retrieval than encoding included bilateral inferior parietal cortex, bilateral precuneus, right frontal polar cortex, right dorsolateral prefrontal cortex, and right inferior frontal/insular cortex.

Ventromedial prefrontal cortex mediates guessing

Guessing is an important component of everyday cognition. The present study examined the neural substrates of guessing using a simple card-playing task in conjunction with functional magnetic resonance imaging (fMRI). Subjects were scanned under four conditions. In two, they were shown images of the back of a playing card and had to guess either the colour or the suit of the card. In the other two they were shown the face of a card and had to report either the colour or the suit. Guessing compared to reporting was associated with significant activations in lateral prefrontal cortex (right more than left), right orbitofrontal cortex, anterior cingulate, bilateral inferior parietal cortex and right thalamus. Increasing the guessing demands by manipulating the number of alternative outcomes was associated with activation of the left lateral and medial orbitofrontal cortex. These data suggest that while simple two choice guessing depends on an extensive neural system including regions of the right lateral prefrontal cortex, activation of orbitofrontal cortex increases as the probabilistic contingencies become more complex. Guessing thus involves not only systems implicated in working memory processes but also depends upon orbitofrontal cortex. This region is not typically activated in working memory tasks and its activation may reflect additional requirements of dealing with uncertainty.

SPECT brain blood flow changes with continuous ligand infusion during previously-learned WCST performance

Performance of the Wisconsin Card Sorting Test (WCST) and related brain-activation patterns reflect both task learning and execution. Normal subjects learned the WCST prior to performance during slow SPECT ligand infusion. Blood flow increased in bilateral inferior frontal, right middle and inferior parietal cortices. Activity decreased in hippocampi, temporal cortex, anterior cingulate and caudate.

Pain processing during three levels of noxious stimulation produces differential patterns of central activity

Previous functional imaging studies have demonstrated a number of discrete brain structures that increase activity with noxious stimulation. Of the commonly identified central structures, only the anterior cingulate cortex shows a consistent response during the experience of pain. The insula and thalamus demonstrate reasonable consistency while all other regions, including the lentiform nucleus, somatosensory cortex and prefrontal cortex, are active in no more than half the current studies. The reason for such discrepancy is likely to be due in part to methodological variability and in part to individual variability. One aspect of the methodology which is likely to contribute is the stimulus intensity. Studies vary considerably regarding the intensity of the noxious and non-noxious stimuli delivered. This is likely to produce varying activation of central structures coding for the intensity, affective and cognitive components of pain. Using twelve healthy volunteers and positron emission tomography (PET), the regional cerebral blood flow (rCBF) responses to four intensities of stimulation were recorded. The stimulation was delivered by a CO 2 laser and was described subjectively as either warm (not painful), pain threshold (just painful), mildly painful or moderately painful. The following group subtractions were made to examine the changing cerebral responses as the stimulus intensity increased: (1) just painful − warm; (2) mild pain − warm; and (3) moderate pain − warm. In addition, rCBF changes were correlated with the subjective stimulus ratings. The results for comparison `1' indicated activity in the contralateral prefrontal (area 10/46/44), bilateral inferior parietal (area 40) and ipsilateral premotor cortices (area 6), possibly reflecting initial orientation and plans for movement. The latter comparisons and correlation analysis indicated a wide range of active regions including bilateral prefrontal, inferior parietal and premotor cortices and thalamic responses, contralateral hippocampus, insula and primary somatosensory cortex and ipsilateral perigenual cingulate cortex (area 24) and medial frontal cortex (area 32). Decreased rCBF was observed in the amygdala region. These responses were interpreted with respect to their contribution to the multidimensional aspects of pain including fear avoidance, affect, sensation and motivation or motor initiation. It is suggested that future studies examine the precise roles of each particular region during the central processing of pain.