Joshua O. Goh

Age and culture modulate object processing and object-scene binding in the ventral visual area.

Behavioral differences in the visual processing of objects and backgrounds as a function of cultural group are well documented. Recent neuroimaging evidence also points to cultural differences in neural activation patterns. Compared with East Asians, Westerners’ visual processing is more object focused, and they activate neural structures that reflect this bias for objects. In a recent adaptation study, East Asian older adults showed an absence of an object-processing area but normal adaptation for background areas. In the present study, 75 young and old adults (half East Asian and half Western) were tested in an fMR-adaptation study to examine differences in object and background processing as well as object—background binding. We found equivalent background processing in the parahippocampal gyrus in all four groups, diminished binding processes in the hippocampus in elderly East Asians and Westerners, and diminished object processing in elderly versus young adults in the lateral occipital complex. Moreover, elderly East Asians showed significantly less adaptation response in the object areas than did elderly Westerners. These findings demonstrate the malleability of perceptual processes as a result of differences in cohort-specific experiences or in cultural exposure over time.

Neuroplasticity and cognitive aging: The scaffolding theory of aging and cognition

A recent proposal called the Scaffolding Theory of Cognitive Aging (STAC) postulates that functional changes with aging are part of a lifespan process of compensatory cognitive scaffolding that is an attempt to alleviate the cognitive declines associated with aging. Indeed, behavioral studies have shown that aging is associated with both decline as well as preservation of selective cognitive abilities. Similarly, neuroimaging studies have revealed selective changes in the aging brain that reflect neural decline as well as compensatory neural recruitment. While aging is associated with reductions in cortical thickness, white-matter integrity, dopaminergic activity, and functional engagement in posterior brain regions such as the hippocampus and occipital areas, there are compensatory increases in frontal functional engagement that correlate with better behavioral performance in older adults. In this review, we discuss these age-related behavioral and brain findings that support the STAC model of cognitive scaffolding and additionally integrate the findings on neuroplasticity as a compensatory response in the aging brain. As such, we also examine the impact of external experiences in facilitating neuroplasticity in older adults. Finally, having laid the foundation for STAC, we briefly describe a proposed intervention trial (The Synapse Program) designed to evaluate the behavioral and neural impact of engagement in lifestyle activities that facilitates successful cognitive scaffolding using a controlled experiment where older adult participants are randomly assigned to different conditions of engagement.

Word frequency and subsequent memory effects studied using event-related fMRI.

Event-related fMRI was used to evaluate the effect of printed word frequency on the subsequent recognition of words incidentally encoded while 16 healthy right-handed volunteers performed living/nonliving judgments. Semantic judgment took longer for low-frequency words. These words were more accurately recognized than high-frequency words at later testing. Low-frequency words were also associated with relatively greater left prefrontal, left fusiform gyrus, and anterior cingulate activation. Words that were subsequently recognized were associated with greater activation in the left prefrontal region compared to those that were forgotten. These findings suggest the specific brain regions where less commonly encountered words are processed in a manner that facilitates their subsequent recognition.

Cultural differences in the lateral occipital complex while viewing incongruent scenes

Converging behavioral and neuroimaging evidence indicates that culture influences the processing of complex visual scenes. Whereas Westerners focus on central objects and tend to ignore context, East Asians process scenes more holistically, attending to the context in which objects are embedded. We investigated cultural differences in contextual processing by manipulating the congruence of visual scenes presented in an fMR-adaptation paradigm. We hypothesized that East Asians would show greater adaptation to incongruent scenes, consistent with their tendency to process contextual relationships more extensively than Westerners. Sixteen Americans and 16 native Chinese were scanned while viewing sets of pictures consisting of a focal object superimposed upon a background scene. In half of the pictures objects were paired with congruent backgrounds, and in the other half objects were paired with incongruent backgrounds. We found that within both the right and left lateral occipital complexes, Chinese participants showed significantly greater adaptation to incongruent scenes than to congruent scenes relative to American participants. These results suggest that Chinese were more sensitive to contextual incongruity than were Americans and that they reacted to incongruent object/background pairings by focusing greater attention on the object.

Culture differences in neural processing of faces and houses in the ventral visual cortex

Behavioral and eye-tracking studies on cultural differences have found that while Westerners have a bias for analytic processing and attend more to face features, East Asians are more holistic and attend more to contextual scenes. In this neuroimaging study, we hypothesized that these culturally different visual processing styles would be associated with cultural differences in the selective activity of the fusiform regions for faces, and the parahippocampal and lingual regions for contextual stimuli. East Asians and Westerners passively viewed face and house stimuli during an functional magnetic resonance imaging experiment. As expected, we observed more selectivity for faces in Westerners in the left fusiform face area (FFA) reflecting a more analytic processing style. Additionally, Westerners showed bilateral activity to faces in the FFA whereas East Asians showed more right lateralization. In contrast, no cultural differences were detected in the parahippocampal place area (PPA), although there was a trend for East Asians to show greater house selectivity than Westerners in the lingual landmark area, consistent with more holistic processing in East Asians. These findings demonstrate group biases in Westerners and East Asians that operate on perceptual processing in the brain and are consistent with previous eye-tracking data that show cultural biases to faces.

Both left and right posterior parietal activations contribute to compensatory processes in normal aging

Older adults often exhibit greater brain activation in prefrontal cortex compared to younger adults, and there is some evidence that this increased activation compensates for age-related neural degradation that would otherwise adversely affect cognitive performance. Less is known about aging and compensatory recruitment in the parietal cortex. In this event-related functional magnetic resonance imaging study, we presented healthy young and old participants with two Stroop-like tasks (number magnitude and physical size). In young, the number magnitude task activated right parietal cortex and the physical size task activated left parietal cortex. In older adults, we observed contralateral parietal recruitment that depended on the task: in the number magnitude task older participants recruited left posterior parietal cortex (in addition to the right parietal activity observed in young) while in the physical size task they recruited right (in addition to left) posterior parietal cortex. In both cases, the additional parietal activity was associated with better performance suggesting that it played a compensatory role. Older adults also recruited left prefrontal cortex during both tasks and this common activation was also associated with better performance. The results provide evidence for task-specific compensatory recruitment in parietal cortex as well as task-independent compensatory recruitment in prefrontal cortex in normal aging.

Investigation and Validation of Intersite fMRI Studies Using the Same Imaging Hardware

To provide a between‐site comparison of functional MRI (fMRI) signal reproducibility in two laboratories equipped with identical imaging hardware and software. Many studies have looked at within‐subject reliability and more recent efforts have begun to calibrate responses across sites, magnetic field strengths, and software. By comparing identical imaging hardware and software, we provide a benchmark for future multisite comparisons.

Culture sculpts the perceptual brain.

Cultural differences in the way Westerners and East Asians perceive and attend to visual objects and contexts have now been shown across many behavioral studies. Westerners display more attention to objects and their features, in line with an analytic processing style, whereas East Asians attend more to contextual relationship, reflecting holistic processing. In this article, we review these behavioral differences and relate them to neuroimaging studies that show the impact of cultural differences even on ventral visual processing of objects and contexts. We additionally consider the evidence showing how extended experience within a culture via aging affects ventral visual function. We conclude that the brain findings are in agreement with the analytic/holistic dichotomy of Western and East Asian visual processing styles. Westerners engage greater object-processing activity while East Asians engage more context-processing activity in the ventral visual areas of the brain. Although such cultural imaging studies are still few, they provide important early evidence supporting the importance of cultural experiences in sculpting visual processing at the neural level.

Cerebrospinal Fluid Aβ and Tau Level Fluctuation in an Older Clinical Cohort

OBJECTIVE To determine whether cerebrospinal fluid (CSF) biomarkers for Alzheimer disease fluctuate significantly over time in a cohort of older, mildly symptomatic individuals. DESIGN Biomarker validation in a clinical cohort. SETTING University hospital inpatient unit. PARTICIPANTS Ten patients admitted for CSF drainage for diagnostic purposes. MAIN OUTCOME MEASURES The CSF levels of Aβ1-40, Aβ1-42, tau, and phosphorylated tau on threonine 181 (p-tau(181)) were measured every 6 hours for 24 or 36 hours. RESULTS The mean coefficient of variation values for each biomarker assessed in our 10 patients were 5.5% (95% CI, 3.8%-10.0%) for Aβ1-42, 12.2% (9.0%-24.2%) for Aβ1-40, 8.2% (5.7%-15.1%) for total tau, and 11.9% (8.5%-23.0%) for p-tau(181). These values are only slightly higher than the variability in the assay. In addition, no significant circadian fluctuation in any Alzheimer disease biomarker was observed given the limitations of our sampling frequency. CONCLUSION In a cohort of elderly patients, little fluctuation in the levels of important Alzheimer disease biomarkers in lumbar CSF is seen as a function of time.

Greater cortical thinning in normal older adults predicts later cognitive impairment

Cross-sectional studies have shown regional differences in cortical thickness between healthy older adults and patients with Alzheimers disease (AD) or mild cognitive impairment (MCI). We now demonstrate that participants who subsequently develop cognitive impairment leading to a diagnosis of MCI or AD (n = 25) experience greater cortical thinning in specific neuroanatomic regions compared with control participants who remained cognitively normal (n = 96). Based on 8 years of annual magnetic resonance imaging scans beginning an average of 11 years before onset of cognitive impairment, participants who developed cognitive impairment subsequent to the scanning period had greater longitudinal cortical thinning in the temporal poles and left medial temporal lobe compared with controls. No significant regional cortical thickness differences were found at baseline between the 2 study groups indicating that we are capturing a critical time when brain changes occur before behavioral manifestations of impairment are detectable. Our findings suggest that early events of the pathway that leads to cognitive impairment may involve the temporal lobe and that this increased atrophy could be considered an early biomarker of neurodegeneration predictive of cognitive impairment years later.