Biomedical subjects

Chunyan Guo

Publications and source records attributed to Chunyan Guo.

6 recordsLinked to original sources

PubMed2006

Long-lasting and transmission-blocking activity of antibodies to Plasmodium falciparum elicited in mice by protein conjugates of Pfs25.

Malaria is a leading cause of morbidity and mortality, estimated to cause >1 million childhood deaths annually. Plasmodium falciparum causes the most severe form of the disease. There is as yet no licensed vaccine for this disease, despite over a half century of research. In this study, we investigated a transmission-blocking vaccine candidate, the ookinete surface protein Pfs25. Antibodies against Pfs25, drawn in during a bite, can block parasite development in the mosquito midgut, preventing transmission to other individuals. Pfs25 is a low-molecular-weight protein, by itself not immunogenic. To increase its immunogenicity, we investigated several methods of conjugating Pfs25 to itself and to other proteins: recombinant Pseudomonas aeruginosa exotoxin A, and ovalbumin, using amide, hydrazone, or thioether linkages. All conjugates were immunogenic and induced booster responses in mice. The scheme to form amide bonds between proteins by using adipic acid dihydrizide as a linker produced the most immunogenic conjugates. Adsorption of the conjugates onto aluminum hydroxide further increased the antibody response. Remarkably, the antibody levels 3 or 7 months after the last injection were significantly higher than those 1 wk after that injection. The observed transmission-blocking activity of immune sera correlated with antibody levels measured by ELISA.

ADP Ribose Transferases↗

PubMed2006

Age effects on brain activity during repetition priming of targets and distracters.

The effects of age on repetition priming and how such differences were related to intentional learning and working memory status were examined. Fourteen older (age 65-75) and 14 younger (age 18-28) healthy adults performed a modified delayed match-to-sample task consisting of a target object held in mind followed by nine test objects. Sixty four-channel EEGs were recorded as participants indicated whether each test object was the same or different from the target object. Half of all target and distractor objects were intentionally studied prior to the task, and both target and distractor objects were repeatedly presented up to four times in each trial. Although both age groups showed repetition priming effects, speed increases due to repetition were more enhanced for elderly. ERP repetition effects for both younger and older adults were indexed via early (200-550) and late (550-850 ms) components. The early repetition effect was affected by whether a distractor was previously studied or not for younger but not for older adults. In contrast, the late repetition effect was not affected by prior intentional learning, and a marginal age effect suggested that repetitions of distractors likely affected older and younger adults differently. These findings suggest that at least two distinguishable repetition mechanisms differentially affect adult aging.

Adolescent↗

PubMed2006

Electrophysiological correlates of visual affective priming.

The present study used event-related potentials (ERPs) to investigate the underlying neural mechanisms of visual affective priming. Eighteen young native English-speakers (6 males, 12 females) participated in the study. Two sets of 720 prime-target pairs (240 affectively congruent, 240 affectively incongruent, and 240 neutral) used either words or pictures as primes and only words as targets. ERPs were recorded from 64 scalp electrodes while participants pressed either "Happy" or "Sad" buttons to indicate target pleasantness. The response time (RT) results confirmed an affective priming effect, with faster responses to affectively congruent trials (659 ms) than affectively incongruent trials (690 ms). Affectively incongruent trials had larger and more negative N200 activation than those to neutral trials. Importantly, a delayed N400 for word prime-target pairs matched the RT results with larger negative amplitudes for incongruent than congruent pairs. This finding suggests that the N400 component is not only sensitive to semantic mismatches, but is also sensitive to affective mismatches for word prime-target pairs.

Adult↗

PubMed2006

Distinguishing source memory and item memory: brain potentials at encoding and retrieval.

Vivid memory for an episode generally includes memory for a central object or event plus memory for background context or source information. To assess neural differences between source and item memory, we used event-related potentials (ERPs) to monitor relevant memory processes at both encoding and retrieval. Participants fluent in Chinese studied Chinese words superimposed on a square or circular background during the study phase, followed by a 1-min delay. Then, memory was tested for both the words (items) and the corresponding background (source), or, in other blocks, tested for the words alone. ERPs to study-phase words differed as a function of whether the word was later remembered. These Dm effects in the interval from 400 to 600 ms, however, did not differ according to whether or not source was remembered. In contrast, ERPs to test-phase words showed clear old/new effects that did differ across conditions. When both item and source were remembered accurately, old/new effects emerged earlier and were larger in amplitude than when source memory was either incorrect or not queried. These results demonstrate that encoding processes indexed by ERPs may have primarily reflected encoding of the visual and semantic properties of these words, stressing item memory over source memory. Retrieval processes indexed by ERPs, in contrast, likely reflected a combination of item retrieval, source retrieval, and related processing engaged when people were remembering words seen earlier.

Adolescent↗

PubMed2005

Electrophysiological correlates of forming memories for faces, names, and face-name associations.

The ability to put a name to a face is a vital aspect of human interaction, but many people find this extremely difficult, especially after being introduced to someone for the first time. Creating enduring associations between arbitrary stimuli in this manner is also a prime example of what patients with amnesia find most difficult. To help develop a better understanding of this type of memory, we sought to obtain measures of the neural events responsible for successfully forming a new face-name association. We used event-related potentials (ERPs) extracted from high-density scalp EEG recordings in order to compare (1) memory for faces, (2) memory for names, and (3) memory for face-name associations. Each visual face appeared simultaneously with a unique spoken name. Signals observed 200-800 ms after the onset of face-name pairs predicted subsequent memory for faces, names, or face-name associations. Difference potentials observed as a function of subsequent memory performance were not identical for these three memory tests, nor were potentials predicting associative memory equivalent to the sum of potentials predicting item memory, suggesting that different neural events at the time of encoding are relevant for these distinct aspects of remembering people.

Adolescent↗

PubMed2004

An electrophysiological investigation of memory encoding, depth of processing, and word frequency in humans.

Memory encoding can be studied by monitoring brain activity correlated with subsequent remembering. To understand brain potentials associated with encoding, we compared multiple factors known to affect encoding. Depth of processing was manipulated by requiring subjects to detect animal names (deep encoding) or boldface (shallow encoding) in a series of Chinese words. Recognition was more accurate with deep than shallow encoding, and for low- compared to high-frequency words. Potentials were generally more positive for subsequently recognized versus forgotten words; for deep compared to shallow processing; and, for remembered words only, for low- than for high-frequency words. Latency and topographic differences between these potentials suggested that several factors influence the effectiveness of encoding and can be distinguished using these methods, even with Chinese logographic symbols.

Adult↗