Differences In Cortical Activity Research Articles

Recognition memory for studied words is determined by cortical activation differences at encoding but not during retrieval

Prior work has shown that when responses to incidentally encoded words are sorted, subsequently remembered words elicit greater left prefrontal BOLD signal change relative to forgotten words. Similarly, low-frequency words elicit greater activation than high-frequency words in the same left prefrontal regions, contributing to their better subsequent memorability. This study examined the relative contribution of encoding and retrieval processes to the correct recognition of target words. A mixture of high- and low-frequency words was incidentally encoded. Scanning was performed at encoding as well as during retrieval. During encoding, greater activation in the left prefrontal and anterior cingulate regions predicted a higher proportion of hits for low-frequency words. However, data acquired during recognition showed that word frequency did not modulate activation in any of the areas tracking successful recognition. This result demonstrates that under some circumstances, the recognition of studied words is determined purely by processes that are active during encoding. In contrast to the finding for hits, activation associated with correctly rejected foils was modulated by word frequency, being higher for high-frequency words in the left lateral parietal and anterior prefrontal regions. These findings were replicated in two further experiments, one in which the number of test items at recognition was doubled and another where encoding strength for high-frequency words was varied (once vs. 10 times). These results indicate that word frequency modulates activity in the left lateral parietal and anterior prefrontal regions contingent on whether the item involved is correctly recognized as a target or a foil. This observation is consistent with a dual process account of episodic memory.

FMRI of two measures of phonological processing in visual word recognition: Ecological validity matters

Previous functional magnetic resonance imaging (fMRI) studies have investigated the role of phonological processing by utilizing nonword rhyming decision tasks (e.g., Pugh et al., 1996). Although such tasks clearly engage phonological components of visual word recognition, it is clear that decision tasks are more cognitively involved than the simple overt naming tasks, which more closely map onto normal reading behavior. Our research aim for this study was to examine the advantages of overt naming tasks for fMRI studies of word recognition processes. Process models are presented to highlight the similarities and differences between two cognitive tasks that are used in the word recognition literature, pseudohomophone naming (e.g., pronounce BRANE) and rhyming decision (e.g., do LEAT and JEAT rhyme?). An fMRI study identified several differences in cortical activation associated with the differences observed in the process models. Specifically, the results show that the overt naming task involved the insular cortex and inferior frontal gyrus, whereas the rhyming decision task engaged the temporal–parietal regions. It is argued that future fMRI research examining the neuroanatomical components of basic visual word recognition utilize overt naming tasks.

Cortical excitability changes associated with musical tasks: a transcranial magnetic stimulation study in humans

Neuroimaging studies have suggested differences in cortical activation in human vocalization and musical tasks. However, functional neurophysiological evidence on cortical excitability changes is lacking. We utilized transcranial magnetic stimulation to demonstrate changes in cortical excitability during overt humming and singing tasks. The findings complement those from neuroimaging and support the existence of separate bilateral deep-seated neural networks, as distinct from those for vocalization.

Cortical excitability changes associated with musical tasks: a transcranial magnetic stimulation study in humans

Neuroimaging studies have suggested differences in cortical activation in human vocalization and musical tasks. However, functional neurophysiological evidence on cortical excitability changes is lacking. We utilized transcranial magnetic stimulation to demonstrate changes in cortical excitability during overt humming and singing tasks. The findings complement those from neuroimaging and support the existence of separate bilateral deep-seated neural networks, as distinct from those for vocalization.

Individual differences in prefrontal cortical activation on the Tower of London planning task: implication for effortful processing.

Solving challenging ('effortful') problems is known to involve the dorsal and dorsolateral prefrontal cortex in normal volunteers, although there is considerable individual variation. In this functional magnetic resonance imaging study, we show that healthy subjects with different levels of performance in the Tower of London planning task exhibit different patterns of brain activation. All subjects exhibited significant bilateral activation in the dorsolateral prefrontal cortex, the anterior and posterior cingulate areas and the parietal cortex. However, 'standard performers' (performance < 70% correct) and 'superior performers' (performance >70% correct) differed in the patterns of activation exhibited. Superior performers showed a significantly more spatially extended activation in the left dorsolateral prefrontal cortex than did standard performers, whereas the latter group tended to show increased activation of the anterior cingulate region.

Hipersensibilidad visceral: Un concepto a nuestro alcance

Despite significant advances in the recognition of etiological factors and pathological mechanisms, the pathophysiology of functional gastrointestinal disorders (FGD) is still not fully understood. Visceral hypersensitivity has been recognized as a characteristic of patients with FGD, especially in patients with irritable bowel syndrome (IBS). Visceral afferent input is modulated by a variety of mechanisms, operating between the gastrointestinal tract and the brain. Dysfunction of these regulatory mechanisms could distort gastrointestinal perceptions. Recent findings suggest that in the majority of cases of IBS the primary abnormality may be at the periphery with alterations of the motor and secretory sensory activity. Although imaging techniques indicate that there are also differences in cortical activation. Furthermore, selective serotonin reuptake inhibitors may benefit FGD. Recent pharmacological studies suggest that 5-HT3 antagonist such as alosetron and cilansetron, and 5-HT4 agonist such as legaserod and prucalopride may also have a potential use in FGD.

Temperament, tympanum, and temperature: four provisional studies of the biobehavioral correlates of tympanic membrane temperature asymmetries.

Previous research in both humans and nonhuman primates suggests that subtle asymmetries in tympanic membrane (TM) temperatures may be related to aspects of cognition and socioaffective behavior. Such associations could plausibly reflect lateralities in cerebral blood flow that support side-to-side differences in regional cortical activation. Asymmetries in activation of the left and right frontal cortex, for example, are correlates of temperamental differences in child behavior and markers of risk status for affective and anxiety disorders. Tympanic membrane temperatures might thus reflect the neural asymmetries that subserve individual differences in temperament and behavior. This report merged findings from four geographically and demographically distinctive studies, which utilized identical thermometry methods to examine associations between TM temperature asymmetries and biobehavioral attributes of 4- to 8-year-old children (N = 468). The four studies produced shared patterns of associations that linked TM temperature lateralities to individual differences in behavior and socioaffective difficulties. Warmer left TMs were associated with "surgent," affectively positive behaviors, whereas warmer right TMs were related to problematic, affectively negative behaviors. Taken together, these findings suggest that asymmetries in TM temperatures could be associated with behavior problems that signal risk for developmental psychopathology.

Age differences in cortical activation during the Kana recognition test with fMRI

Fifty-six Japanese university students completed two blocks of trials in which each trial involved presentation of Hiragana and Katakana (Japanese syllabary) strings requiring a lexical classification.In the first block, subjects were presented words and non-words written in either Hiragana or Katakana. In the second block, the original words were repeated in either the same orthography or in the alternative orthography. In this block, the repeated words were mixed with new words and new non-words.Subjects were assigned in each of the four groups given by the factorial combination of types of Kana shape and presentation under first and second.Reaction time in the lexical classification was facilitated both when words were repeated in the same orthography and when repeated in the different orthography, but size of the facilitation of the former was significantly greater than that of the latter condition.The results suggest the view that lexical representations of Hiragana and Katakana did not completely overlap; rather, they share some common aspects of the lexicon.

Behavioral challenges and functional imaging: Where the rubber meets the road

Behavioral challenges and functional imaging: Where the rubber meets the road

Age differences in prefrontal cortical activity in working memory.

Age differences in prefrontal cortical activity in working memory.

Interhemispheric asymmetry of motor cortical excitability in major depression as measured by transcranial magnetic stimulation.

Neuroimaging studies of major depressive disorder (MDD) indicate interhemispheric differences in prefrontal cortical activity (right greater than left). To investigate whether there are any interhemispheric differences of motor cortical excitability in MDD. Eight patients with treatment-refractory MDD off medication were assessed for the severity of their depression, and transcranial magnetic stimulation studies (bilateral motor threshold and paired-pulse studies) were conducted. Eight normal controls were also studied. MDD patients showed significant interhemispheric differences in motor threshold and paired-pulse curves, both of which showed lower excitability on the left hemisphere. Such differences were absent in controls. Our findings may aid the further understanding of the neurophysiology underlying MDD.

Neuro-cognitive activity during a self-paced visuospatial task: comparative EEG profiles in marksmen and novice shooters

Log-transformed EEG power spectral estimates (6–7, 9,10–11,18–22, and 36–44 Hz), obtained from skilled marksmen and novice shooters at sites F3, F4, C3, C4,T3, T4, P3, P4, O1, and O2 during the aiming period (6 s) of a target shooting task for each of 40 trials up to the moment of trigger pull, were contrasted to determine regional differences in cortical activation. The EEG power obtained from both groups during the preparatory aiming period was also compared to that observed for a similar time period during the processing of standard verbal and spatial tasks. The marksmen exhibited less activation than the novice shooters at all sites during the aiming period with a pronounced difference in the left central-temporal-parietal area. Fewer group differences in cortical activation were observed during the comparative verbal and spatial tasks with which the groups held equal experience. Additionally, the novice shooters exhibited a cortical activation pattern during target shooting that was similar to that observed during the processing of the comparative verbal and spatial tasks. In contrast, marksmen generally exhibited less cortical activation during the aiming period when contrasted to that during the novel comparative tasks. These results are consistent with the notion of relative economy in the cortical processes of marksmen, relative to controls, during the specific challenge with which they are highly practiced.

Age-related differences in visual perception: a PET study

To assess age-related differences in cortical activation during form perception, two classes of visual textures were shown to young and older subjects undergoing positron emission tomography (PET). Subjects viewed even textures that were rich in rectangular blocks and extended contours and random textures that lacked these organized form elements. Within-group significant increases in regional cerebral blood flow (rCBF) during even stimulation relative to random stimulation in young subjects were seen in occipital, inferior and medial temporal regions, and cerebellum, and in older subjects, in posterior occipital and frontal regions. Group by texture type interactions revealed significantly smaller rCBF increases in older subjects relative to young in occipital and medial temporal regions. These results indicate that young subjects activate the occipitotemporal pathway during form perception, whereas older subjects activate occipital and frontal regions. The between-group differences suggest that age-related reorganization of cortical activation occur during early visual processes in humans.

Expertise Differences in Cortical Activation and Gaze Behavior during Rifle Shooting

The purpose of this study was to examine whether variability in gaze behavior and cortical activation would differentiate expert (n = 12) and nonexpert (n = 13) small-bore rifle shooters. Spectral-activity and eye-movement data were collected concurrently during the course of a regulation indoor sequence of 40 shots from the standing position. Experts exhibited significantly superior shooting performance, as well as a significantly longer quiet eye period preceding shot execution than did nonexperts. Additionally, expertise interacted with hemispheric activation levels: Experts demonstrated a significant increase in left-hemisphere alpha and beta power, accompanied by a reduction in right-hemisphere alpha and beta power, during the preparatory period just prior to the shot. Nonexperts exhibited similar hemispheric asymmetry, but to a lesser extent than did experts. Findings suggest systematic expertise-related differences in ocular and cortical activity during the preparatory phase leading up to the trigger pull that reflects more optimal organization of the neural structures needed to achieve high-level performance.

Differences in frontal cortical activation by a working memory task after substitution of risperidone for typical antipsychotic drugs in patients with schizophrenia.

Antipsychotic drug treatment of schizophrenia may be complicated by side effects of widespread dopaminergic antagonism, including exacerbation of negative and cognitive symptoms due to frontal cortical hypodopaminergia. Atypical antipsychotics have been shown to enhance frontal dopaminergic activity in animal models. We predicted that substitution of risperidone for typical antipsychotic drugs in the treatment of schizophrenia would be associated with enhanced functional activation of frontal cortex. We measured cerebral blood oxygenation changes during periodic performance of a verbal working memory task, using functional MRI, on two occasions (baseline and 6 weeks later) in two cohorts of schizophrenic patients. One cohort (n = 10) was treated with typical antipsychotic drugs throughout the study. Risperidone was substituted for typical antipsychotics after baseline assessment in the second cohort (n = 10). A matched group of healthy volunteers (n = 10) was also studied on a single occasion. A network comprising bilateral dorsolateral prefrontal and lateral premotor cortex, the supplementary motor area, and posterior parietal cortex was activated by working memory task performance in both the patients and comparison subjects. A two-way analysis of covariance was used to estimate the effect of substituting risperidone for typical antipsychotics on power of functional response in the patient group. Substitution of risperidone increased functional activation in right prefrontal cortex, supplementary motor area, and posterior parietal cortex at both voxel and regional levels of analysis. This study provides direct evidence for significantly enhanced frontal function in schizophrenic patients after substitution of risperidone for typical antipsychotic drugs, and it indicates the potential value of functional MRI as a tool for longitudinal assessment of psychopharmacological effects on cerebral physiology.

Differences in human visual evoked potentials during the perception of colour as revealed by a bootstrap method to compare cortical activity. A prospective study

The aim of this prospective study was to investigate the colour related information in cortical activity as it is recorded from the scalp, by comparing the shape of the potential fields. Six healthy volunteers and two volunteers with known protanopsia were used to record multichannel visual evoked potentials after stimulation with chromatic stimuli of equally perceived brightness. The scalp fields resulting from each of the four chromatic stimuli were compared in pairs, in every possible combination and for each time point, using Efron's bootstrap method. It was found that, in comparison to other stimuli responses, the long dominant wavelength stimulus results in significant differences of cortical activity. These are mainly identified in two time periods: (a) at mid-latency responses, usually during the onset and development of P100 component, and (b) after the peak (on the decline) of P100 component. Similar but less evident behaviour was identified when the responses from the short dominant wavelength stimulus were compared with those from the other stimuli. Colour effects were not significant in protanops. The proposed method can be used to locate in time and quantify the differences in cortical activity during colour perception.

Vibrissae-Evoked Behavior and Conditioning before Functional Ontogeny of the Somatosensory Vibrissae Cortex

The following experiments determined that the somatosensory whisker system is functional and capable of experience-dependent behavioral plasticity in the neonate before functional maturation of the somatosensory whisker cortex. First, unilateral whisker stimulation caused increased behavioral activity in both postnatal day (P) 3-4 and P8 pups, whereas stimulation-evoked cortical activity (14C 2-deoxyglucose autoradiography) was detectable only in P8 pups. Second, neonatal rat pups are capable of forming associations between whisker stimulation and a reinforcer. A classical conditioning paradigm (P3-P4) showed that the learning groups (paired whisker stimulation-shock or paired whisker stimulation-warm air stream) exhibited significantly higher behavioral responsiveness to whisker stimulation than controls. Finally, stimulus-evoked somatosensory cortical activity during testing [P8; using 14C 2-deoxyglucose (2-DG) autoradiography] was assessed after somatosensory conditioning from P1-P8. No learning-associated differences in stimulus-evoked cortical activity were detected between learning and nonlearning control groups. Together, these experiments demonstrate that the whisker system is functional in neonates and capable of experience-dependent behavioral plasticity. Furthermore, in contrast to adult somatosensory classical conditioning, these data suggest that the cortex is not required for associative somatosensory learning in neonates.

Developmental and regional differences in nitric oxide synthase activity and blood flow in the sheep brain.

Nitric oxide synthase (NOS) participates in the regulation of cerebral blood flow and neurotransmitter release and as a second messenger of glutamatergic and cholinergic systems. Developmental differences in NOS activity have been described in the rat, but not in a species with longer gestation and a larger, lobulated brain at birth. We assayed NOS activity by conversion of [14C]L-arginine to [14C]L-citrulline in 50-mg tissue samples from eight brain regions in sheep at 70, 92, 110, and 135 days gestation (term = 145 days); newborns (< 7 days); and adults to test the hypothesis that NOS activity in the brain is developmentally regulated from midgestation through adulthood and matures along the neuroaxis in parallel with the known development of cerebral blood flow and neuronal activity. Three patterns of maturation of NOS activity were evident: increasing to or exceeding adult levels before 70 days gestation in the thalamus, cerebellum, and medulla; increasing to adult levels between 70 and 92 days in the hippocampus; and increasing to adult levels after 92 days in the cortex and caudate. Additionally, there were regional differences in cortical NOS activity: at 70 and 92 days of gestation, frontal cortex NOS activity was greater than parietal or occipital activity, and at 135 days gestation and in the newborn and adult, cortical and caudate activity exceeded that in most of the more caudal regions. The up to fourfold increase in regional cortical NOS activity between 92 and 135 days gestation was associated with twofold increases in cerebral blood flow and oxygen consumption during this period. Inhibition of NOS activity with administration of 60 mg/kg of NG-nitro-L-arginine methylester (L-NAME) resulted in 27% and 25% reductions in cerebral blood flow at 93 and 133 days gestation. While the associated increases in NOS activity with increases in CBF and CMRO2 do not appear causative, at various points in gestation the development of NOS activity may participate in the development of mature patterns of cerebral blood flow regulation in parallel with development of synaptic and electrical activity.

Strength as a factor influencing mirror movements

A finger flexion task was used to investigate intensity of mirror movement. Subjects were asked to maintain target forces, with either their index or small finger, that represented 25, 50 or 75 percent of their maximum strength capacity for the finger performing the task. Relative to the force produced, males and females exhibited the same amount of mirror movement. However, mirror movement relative to force exerted was greater when the left hand performed the task, a finding consistent with previous research. Greater amounts of mirror movement were recorded for movements of the small finger compared to the index finger, consistent with the cortical activation explanation (Todor and Lazarus, 1986). These results suggest that strength differences are not the principal determinant of intensity of mirror movement. Rather, differing functional roles of the hands and fingers, reflecting differences in cortical activation and organisation, appear to mediate the intensity of mirror movement occurrence.

PS-14-7 Movement-related cortical potentials upon forward stepping — difference by varied trigger points —

The aim of this study was to assess the influence of age-related changes in cortical activity related to the motor preparation involved in simple- and discriminative-reaction tasks. To distinguish between age effects on motor planning and stimulus processing, both movement- and stimulus-locked event related potentials (ERPs) were investigated in 14 younger, 14 middle-aged, and 14 older adults (mean ages 24.4, 49, and 70 years, respectively). The novel results of the present study are the prefrontal over-recruitment observed in older adults in movement-related cortical potentials (MRCPs) and the differential pattern of aging effects observed at behavioral and at electrophysiological level between middle-aged and older adults. Overall, the following results were observed: (i) behavioral results confirmed the well-known slowing of responses in aging people, which were associated with optimal accuracy; (ii) the age-related differences in cortical activity underlying the generation of voluntary movements in response to external stimuli were more pronounced for the motor planning than the stimulus processing stage; (iii) the source and the time-course analysis of the over-recruitment in the older adults indicated tonic involvement of prefrontal areas regardless of task complexity; and (iv) middle-aged adults showed a ‘young adult-like’ behavioral speed, but an ‘older adult-like’ overactivation of prefrontal areas. In summary, to reach the same accuracy, older subjects prepared the action with greater anticipation and higher cost, as indexed by the earlier latency onset and larger prefrontal cortical activation.