Prefrontal lesions impair object-spatial integration.

Authors:

• Bradley Voytek

• Maryam Soltani

• Natasha Pickard

• Mark M. Kishiyama

• Robert T. Knight

Date: 2012

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Abstract:

How and where object and spatial information are perceptually integrated in the brain is a central question in visual cognition. Single-unit physiology, scalp EEG, and fMRI research suggests that the prefrontal cortex (PFC) is a critical locus for object-spatial integration. To test the causal participation of the PFC in an object-spatial integration network, we studied ten patients with unilateral PFC damage performing a lateralized object-spatial integration task. Consistent with single-unit and neuroimaging studies, we found that PFC lesions result in a significant behavioral impairment in object-spatial integration. Furthermore, by manipulating inter-hemispheric transfer of object-spatial information, we found that masking of visual transfer impairs performance in the contralesional visual field in the PFC patients. Our results provide the first evidence that the PFC plays a key, causal role in an object-spatial integration network. Patient performance is also discussed within the context of compensation by the non-lesioned PFC.

Damage to the prefrontal cortex impairs familiarity but not recollection memory

Authors:

• Mariam Aly

• Andrew P. Yonelinas

• Mark M. Kishiyama

• Robert T. Knight

Date: 2011

PubMed: 21827792

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Abstract:

Frontal lobe lesions impair recognition memory but it is unclear whether the deficits arise from impaired recollection, impaired familiarity, or both. In the current study, recognition memory for verbal materials was examined in patients with damage to the left or right lateral prefrontal cortex. Words were incidentally encoded under semantic or phonological orienting conditions, and recognition memory was tested using a 6-point confidence procedure. Receiver operating characteristics (ROCs) were examined in order to measure the contributions of recollection and familiarity to recognition memory. In both encoding conditions, lateral prefrontal cortex damage led to a deficit in familiarity but not recollection. Similar deficits were observed in left and right hemisphere patients. The results indicate that the lateral prefrontal cortex plays a critical role in the monitoring or decision processes required for accurate familiarity-based recognition responses.

Poverty, stress and cognitive functioning

Authors:

• Mark M. Kishiyama

• Robert T. Knight

Date: 2010

Abstract:

Social inequalities in income and wealth have a profound effect on the physical and mental health of children. For example, children from low-socioeconomic-status (SES) backgrounds are at greater risk for most forms of childhood morbidities compared to children from higher-SES backgrounds. [Note that the determination of SES is based on varying indices of family income (in relation to federally determined poverty thresholds), parental education (for example, those with college degrees versus those without), and parental occupation (for example, professional versus unskilled labor)]. Impoverished conditions during childhood are associated with poorer adult health, and low childhood SES may be the single most powerful contributor to premature mortality and morbidity worldwide. Significant relationships have been observed between SES and cognitive ability and between SES and academic achievement in childhood. In fact, SES has a stronger relationship with cognitive performance than does physical health. Children from low-SES backgrounds perform below children from higher-SES backgrounds on tests of intelligence and academic achievement. In addition, SES has been found to have a major effect on language development. For example, one study found that the average vocabulary size of 3-year-old children from families receiving welfare was less than half the size of the average vocabulary of children from higher-SES (professional) families. Low-SES children are also more likely to fail courses, be placed in special education, and drop out of high school compared to high-SES children.

Multimodal effects of local context on target detection: evidence from P3b

Authors:

• Noa Fogelson

• Xue Wang

• Jeffrey B. Lewis

• Mark M. Kishiyama

• Mingzhou Ding

• Robert T. Knight

Date: 2009

DOI: 10.1162/jocn.2009.21071

PubMed: 18702574

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Abstract:

We used the P300 component to investigate how changes in local context influenced the ability to detect target stimuli. Local context was defined as the occurrence of a short predictive series of stimuli before delivery of a target event. EEG was recorded in 12 subjects during auditory and visual sessions. Stimuli were presented in the center of the auditory and visual field and consisted of 15% targets (1000 Hz tone or downward facing triangle) and 85% of equal amounts of three types of standards (1500, 2000, and 2500 Hz tones or triangles facing left, upward, and right). Recording blocks consisted of targets preceded by either randomized sequences of standards or by sequences including a three-standard predictive sequence signaling the occurrence of a subsequent target event. Subjects pressed a button in response to targets. Peak target P300 (P3b) amplitude and latency were evaluated for targets after predictive and nonpredictive sequences using conventional averaging and a novel single-trial analysis procedure. Reaction times were shorter for predictable targets than for nonpredicted targets. P3b latency was shorter for predicted targets than for nonpredictive targets, and there were no significant P3b amplitude differences between predicted and random targets, as determined by both conventional averaging and single-trial analysis. Comparable effects on amplitude and latency were observed in both the auditory and visual modalities. The results indicate that local context has differential effects on P3b amplitude and latency, and exerts modality-independent effects on cognitive processing.

Novelty Enhancements in Memory Are Dependent on Lateral Prefrontal Cortex

Authors:

• Mark M. Kishiyama

• Andrew P. Yonelinas

• Robert T. Knight

Date: 2009

DOI: 10.1523/JNEUROSCI.5507-08.2009

PubMed: 19553451

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Abstract:

Physiological evidence indicates thatseveral brain regions, including the medial temporal lobes and prefrontal cortex (PFC), are involved in processing events that are novel or distinctive in their immediate context. However, behavioral studies that investigate whether these regions are critical for producing stimulus novelty advantages in memory are limited. For example, evidence from an animal lesion study indicated that the PFC is involved in stimulus novelty effects, but this has not been examined in humans. In the current study, we used a von Restorff novelty paradigm to testa large cohortof lateral PFC patients (n
16). We found thatpatients with lateral PFC damage were impaired in recollection- and familiarity-based recognition, and they did not exhibit a normal memory advantage for novel compared with non-novel items. These results provide neuropsychological evidence supporting a key role for the lateral PFC in producing stimulus novelty advantages in memory.

Socioeconomic disparities affect prefrontal function in children

Authors:

• Mark M. Kishiyama

• W. Thomas Boyce

• Amy M. Jimenez

• Lee M. Perry

• Robert T. Knight

Date: 2009

DOI: 10.1162/jocn.2009.21101

PubMed: 18752394

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Abstract:

Social inequalities have profound effects on the physical and mental health of children. Children from low socioeconomic status (SES) backgrounds perform below children from higher SES backgrounds on tests of intelligence and academic achievement, and recent findings indicate that low SES (LSES) children are impaired on behavioral measures of prefrontal function. However, the influence of socioeconomic disparity on direct measures of neural activity is unknown. Here, we provide electrophysiological evidence indicating that prefrontal function is altered in LSES children. We found that prefrontal-dependent electrophysiological measures of attention were reduced in LSES compared to high SES (HSES) children in a pattern similar to that observed in patients with lateral prefrontal cortex (PFC) damage. These findings provide neurophysiological evidence that social inequalities are associated with alterations in PFC function in LSES children. There are a number of factors associated with LSES rearing conditions that may have contributed to these results such as greater levels of stress and lack of access to cognitively stimulating materials and experiences. Targeting specific prefrontal processes affected by socioeconomic disparity could be helpful in developing intervention programs for LSES children.

The neural substrates of visual implicit memory: do the two hemispheres play different roles?

Authors:

• Neal E. A. Kroll

• Andrew P. Yonelinas

• Mark M. Kishiyama

• Kathleen Baynes

• Robert T. Knight

• Michael S. Gazzaniga

Date: 2003

PubMed: 14511536

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Abstract:

Identification of visually presented words is facilitated by implicit memory, or visual priming, for past visual experiences with those words. There is disagreement over the neuro-anatomical substrates of this form of implicit memory. Several studies have suggested that this form of priming relies on a visual word-form system localized in the right occipital lobe, whereas other studies have indicated that both hemispheres are equally involved. The discrepancies may be related to the types of priming tasks that have been used because the former studies have relied primarily on word-stem completion tasks and the latter on tasks like word-fragment completion. The present experiments compared word-fragment and word-stem measurements of visual implicit memory in patients with right occipital lobe lesions and patients with complete callosotomies. The patients showed normal visual implicit memory on fragment completion tests, but essentially no visual priming on standard stem completion tests. However, when we used a set of word stems that had only one correct solution for each test item, as was true of the items in the fragment completion tests, the patients showed normal priming effects. The results indicate that visual implicit memory for words is not solely dependent upon the right hemisphere, rather it reflects changes in processing efficiency in bilateral visual regions involved in the initial processing of the items. However, under conditions of high lexical competition (i.e., multiple completion word stems), the lexical processes, which are dominant in the left hemisphere, overshadow the visual priming supported by the left hemisphere.