Biomedical subjects

Stefano Cappa

Publications and source records attributed to Stefano Cappa.

6 recordsLinked to original sources

PubMed2005

Functional frontoparietal connectivity during encoding and retrieval processes follows HERA model. A high-resolution study.

Recent neuroimaging studies of long-term episodic memory have suggested that left prefrontal cortex predominates in encoding condition, whereas right prefrontal cortex predominates in retrieval condition (hemispheric encoding and retrieval asymmetry, HERA model). The present electroencephalographic (EEG) study investigated the functional coupling of fronto-parietal regions during long-term memorization of visuo-spatial contents (i.e. landscapes, interiors of apartments), to test the predictions of the HERA model. Global fronto-parietal coupling was estimated by spectral coherence, whereas the "direction" of the fronto-parietal information flow was estimated by directed transfer function (DTF). The EEG rhythms of interest were theta (4-7 Hz), alpha (8-13 Hz), beta (14-30 Hz), and gamma (30-45 Hz). Statistically significant coherence in line with the HERA model was obtained at the gamma band. Namely, the fronto-parietal gamma coherence prevailed in the left hemisphere during the encoding condition and in the right hemisphere during the retrieval condition. The DTF estimates of the gamma band showed a dominant parietal-to-frontal directional flow in the right hemisphere during the encoding condition and in the left hemisphere during the retrieval condition (i.e. hemisphere-condition combination not involved by the HERA model). In contrast, a balanced bidirectional flow of the fronto-parietal coupling was observed in the left hemisphere during the encoding condition and in the right hemisphere during the retrieval condition (i.e. hemisphere-condition combination involved by the HERA model). In conclusion, the present encoding-retrieval conditions induced maximal fronto-parietal gamma coupling with bidirectional information flow in the hemisphere-condition combination predicted by the HERA model.

Alpha Rhythm↗

PubMed2004

Increased periodic arousal fluctuations during non-REM sleep are associated to superior memory.

Sleep has been implicated in the plastic cerebral changes that underlie learning and memory. The scientific investigation of people with exceptional memory has been relatively neglected. We report the results of a polysomnographic investigation of an individual with superior memory performance. The sleep structure, in terms of sleep induction and maintenance, as well as non-REM and REM sleep percentages, were normal. The main finding was an increased number of periodic arousal fluctuations during non-REM sleep (measured as cyclic alternating pattern, CAP) during two consecutive nights (7-8 S.D. units above that observed in age-matched controls). Since CAP rate reflects the structural organization of non-REM sleep, this observation supports the hypothesis of a link between non-REM sleep and declarative memory performance.

Adult↗

PubMed2004

Human cortical EEG rhythms during long-term episodic memory task. A high-resolution EEG study of the HERA model.

Many recent neuroimaging studies of episodic memory have indicated an asymmetry in prefrontal involvement, with the left prefrontal cortex more involved than the right in encoding, the right more than the left in retrieval (hemispheric encoding and retrieval asymmetry, or HERA model). In this electroencephalographic (EEG) high-resolution study, we studied brain rhythmicity during a visual episodic memory (recognition) task. The theta (4-6 Hz), alpha (6-12 Hz) and gamma (28-48 Hz) oscillations were investigated during a visuospatial long-term episodic memory task including an encoding (ENC) and retrieval (RET) phases. During the ENC phase, 25 figures representing interiors of buildings ("indoor") were randomly intermingled with 25 figures representing landscapes ("landscapes"). Subject's response was given at left ("indoor") or right ("landscapes") mouse button. During the RET phase (1 h later), 25 figures representing previously presented "indoor" pictures ("tests") were randomly intermingled with 25 figures representing novel "indoor" ("distractors"). Again, a mouse response was required. Theta and alpha EEG results showed no change of frontal rhythmicity. In contrast, the HERA prediction of asymmetry was fitted only by EEG gamma responses, but only in the posterior parietal areas. The ENC phase was associated with gamma EEG oscillations over left parietal cortex. Afterward, the RET phase was associated with gamma EEG oscillations predominantly over right parietal cortex. The predicted HERA asymmetry was thus observed in an unexpected location. This discrepancy may be due to the differential sensitivity of neuroimaging methods to selected components of cognitive processing. The strict relation between gamma response and perception suggests that retrieval processes of long-term memory deeply impinged upon sensory representation of the stored material.

Adult↗

PubMed2004

The impact of lexical-semantic impairment and of executive dysfunction on the word reading performance of patients with probable Alzheimer dementia.

The influence of lexical-semantic impairment and of executive dysfunction on word naming performance was investigated in a group of patients with probable Alzheimer dementia (AD). The patients, who varied in the severity of the illness, were tested in a word naming task where they had to read aloud Italian three-syllable words with a dominant or subordinate stress pattern. These types of words have been shown to interact with frequency in normal adults [J. Exp. Psychol.: Hum. Percept. Perform. 18 (4) (1992) 987], so that the effect of the subordinate stress pattern (slower reading times) is only apparent for low frequency words. The frequency and stress effects on accuracy increased across dementia severity levels. Regression analyses showed that the impairment in reading low frequency words with subordinate stress depended largely on the level of lexical-semantic impairment, measured by a test of semantic memory and comprehension. Implications for the current reading models are discussed.

Aged↗

PubMed2003

An investigation of semantic errors in unimpaired and Alzheimer's speakers of Italian.

Semantic errors are a common type of slip of the tongue for normal speakers; they are also considered to be the hallmark of progressive diseases that affect semantic memory such as Alzheimer's Disease (AD) and semantic dementia. In unimpaired speakers, semantic errors have been shown to be affected by syntactic variables. For example, Marx (1999) has shown that speakers of a gendered language such as German tend to substitute a target with another word that shares the same grammatical gender with the target more often than chance would predict. This finding suggests that errors occur at a level at which lexical information about the target is activated and retrieved. Here, we assess whether such an effect of syntactic variables (gender) also holds in experimental tasks designed to induce errors in unimpaired speakers of Italian (another gendered language) and whether this effect can also be observed in the semantic errors produced in the same task by AD patients. We found that for the unimpaired speakers, the gender of the target word constrained the error committed, while this was not the case for the AD patients. We take this finding to suggest a different locus for the errors in the two populations: while the semantic errors by the unimpaired speakers occur because of mis-selection of a lexical entry due to lexical competition among semantically similar words, the errors by the AD patients occur because of insufficient activation of lexical representations.

Adult↗

PubMed2003

The breakdown of semantic knowledge: insights from a statistical model of meaning representation.

Investigations of patients with semantic category-specific deficits have revealed a wide range of performance and variability in categories that are impaired or spared; this variability presents a challenge to accounts of category specificity. Accounts based only on impairment to semantic features of a particular type (e.g., visual), as well as accounts based only on featural properties (e.g., feature intercorrelations), are insufficient to explain the variability of patients' performance. A first goal of the paper is to discuss how a hybrid account incorporating both a level of organization according to feature types (a level of nonlinguistic conceptual representations) and a level of organization dictated by featural properties may provide a more comprehensive account of the cases reported in the literature. The second and most novel goal of the study reported here is to derive from our hybrid account a series of novel predictions concerning the representation and impairment of a different domain of knowledge: knowledge of actions and events, a domain of knowledge that has received remarkably little attention to date.

Cognition↗