Prospective memory: the combined impact of cognitive load and task focality.

Prospective Memory (PM) entails a set of executive processes primarily associated with the activation of frontal and parietal regions. Both the number of PM-targets to be monitored (i.e. task load) and the relationship between the type of PM-targets and the ongoing (ONG) task (i.e. task focality) can impact executive monitoring and PM performance. In the present imaging study, we manipulated load and focality of an event-based PM task to test the hypothesis that common resources engage in situations requiring high levels of cognitive control: that is, in high-load (i.e. monitor multiple PM-targets) and non-focal conditions (i.e. monitor at the same time letters' identity and color). We investigated monitoring-related and detection-related processes by assessing behavior and brain activity separately for ONG trials (monitoring) and PM-targets (detection). At the behavioral level, we found a significant interaction between load and focality during detection, with slowest reaction times for focal, high-load PM-targets. The imaging analyses of the detection phase revealed the activation of the left intraparietal sulcus in the high-load conditions. Both in the monitoring and the detection phases, we found overlapping effects of non-focality and low-load in the fusiform gyrus. Our results suggest that under low-load conditions, cognitive control operates via early selection mechanisms in the ventral occipito-temporal cortex. By contrast, high-load conditions entail control at later processing stages within the dorsal parietal cortex. We conclude that load and focality operate via different mechanisms, with the level of task load largely determining how cognitive control selects the most relevant information.

Acute hyperammonaemia induces a sustained decrease in vigilance, which is modulated by caffeine.

UNLABELLED: Hyperammonaemia is observed after prolonged, intense exercise, or in patients with hepatic failure. In the latter, it is associated with a set of neurological and psychiatric abnormalities termed hepatic encephalopathy. THE AIMS OF OUR STUDY WERE: 1. to measure vigilance in a condition of induced hyperammonaemia; 2. to assess whether caffeine modulates the effects of hyperammonaemia on vigilance, if any. Ten healthy volunteers (28.5 ± 5 years; 5 males) underwent three experimental sessions consisting of two-hourly measurements of capillary ammonia, subjective sleepiness (Karolinska Sleepiness Scale) and vigilance (Psychomotor Vigilance Task, PVT), in relation to the intake of breakfast (+/-coffee), an amino acid mixture which induces hyperammonaemia (amino acid challenge; AAC), and AAC+coffee (only for participants who had coffee with their standard breakfast). The AAC resulted in: 1. the expected increase in capillary ammonia levels, with highest values at approximately 4 h after the administration; 2. a significant increase in subjective sleepiness ratings; 3. a sustained increase in PVT-based reaction times. When caffeine was administered after the AAC, both subjective sleepiness and the slowing in RTs were significantly milder than in the AAC-only condition. In conclusion, acute hyperammonaemia induces an increase in subjective sleepiness and a sustained decrease in vigilance, which are attenuated by the administration of a single espresso coffee.

An EEGLAB plugin to analyze individual EEG alpha rhythms using the "channel reactivity-based method".

A recent paper [1] proposed a new technique, termed the channel reactivity-based method (CRB), for characterizing EEG alpha rhythms using individual (IAFs) and channel (CAFs) alpha frequencies. These frequencies were obtained by identifying the frequencies at which the power of the alpha rhythms decreases. In the present study, we present a graphical interactive toolbox that can be plugged into the popular open source environment EEGLAB, making it easy to use CRB. In particular, we illustrate the major functionalities of the software and discuss the advantages of this toolbox for common EEG investigations. The CRB analysis plugin, along with extended documentation and the sample dataset utilized in this study, is freely available on the web at http://bio.dei.unipd.it/crb/.

Insight into the relationship between brain/behavioral speed and variability in patients with minimal hepatic encephalopathy.

OBJECTIVE: Intra-individual variability (IIV) of response reaction times (RTs) and psychomotor slowing were proposed as markers of brain dysfunction in patients with minimal hepatic encephalopathy (MHE), a subclinical disorder of the central nervous system frequently detectable in patients with liver cirrhosis. However, behavioral measures alone do not enable investigations into the neural correlates of these phenomena. The aim of this study was to investigate the electrophysiological correlates of psychomotor slowing and increased IIV of RTs in patients with MHE. METHODS: Event-related potentials (ERPs), evoked by a stimulus-response (S-R) conflict task, were recorded from a sample of patients with liver cirrhosis, with and without MHE, and a group of healthy controls. A recently presented Bayesian approach was used to estimate single-trial P300 parameters. RESULTS: Patients with MHE, with both psychomotor slowing and higher IIV of RTs, showed higher P300 latency jittering and lower single-trial P300 amplitude compared to healthy controls. In healthy controls, distribution analysis revealed that single-trial P300 latency increased and amplitude decreased as RTs became longer; however, in patients with MHE the linkage between P300 and RTs was weaker or even absent. CONCLUSIONS: These findings suggest that in patients with MHE, the loss of the relationship between P300 parameters and RTs is related to both higher IIV of RTs and psychomotor slowing. SIGNIFICANCE: This study highlights the utility of investigating the relationship between single-trial ERPs parameters along with RT distributions to explore brain functioning in normal or pathological conditions.

Failure of hearing screening in high-risk neonates does not increase parental anxiety.

OBJECTIVE: The aim of this study was to determine whether a failure of neonatal hearing screening affected the anxiety level of parents of high-risk infants. METHODS: Two hundred and eighty-eight parents of infants included in the neonatal hearing screening protocol of our Institution were tested with the Spielberger State-Trait Anxiety Inventory and with an open-question questionnaire investigating parents' attitude to hearing problems in their child, done at the time of audiological follow-up. 105 were parents of high-risk infants who had been discharged from neonatal intensive care unit (NICU) and 183 of low-risk infants discharged from well-baby nursery. RESULTS: No differences in anxiety levels were seen between parents of high-risk infants passing and failing neonatal hearing screening using homogeneous case-control pairs. Additionally, no differences in the level of anxiety were found between parents of high- and low-risk infants failing neonatal auditory screening. CONCLUSIONS: Failure of neonatal auditory screening does not affect the anxiety levels of parents of high-risk infants at post discharge from NICU. This finding is a key factor to be considered when evaluating the costs and benefits of tests for universal neonatal hearing screening.

A novel method for the determination of the EEG individual alpha frequency.

The individual alpha frequency (IAF) is one of the most common tools used to study the variability of EEG rhythms among subjects. Several approaches have been proposed in the literature for IAF determination, including the popular peak frequency (PF) method, the extended band (EB) method, and the transition frequency (TF) method. However, literature techniques for IAF determination are over-reliant on the presence of peaks in the EEG spectrum and are based on qualitative criteria that require visual inspection of every individual EEG spectrum, a task that can be time consuming and difficult to reproduce. In this paper a novel channel reactivity based (CRB) method is proposed for IAF computation. The CRB method is based on quantitative indexes and criteria and relies on task-specific alpha reactivity patterns rather than on the presence of peaks in the EEG spectrum. Application of the technique to EEG signals recorded from 19 subjects during a cognitive task demonstrates the effectiveness of the CRB method and its capability to overcome the limits of PF, EB, and TF approaches.

Modulation of a fronto-parietal network in event-based prospective memory: an rTMS study.

Event-based prospective memory (PM) is a multi-component process that requires remembering the delayed execution of an intended action in response to a pre-specified PM cue, while being actively engaged in an ongoing task. Some neuroimaging studies have suggested that both prefrontal and parietal areas are involved in the maintenance and realization of delayed intentions. In the present study, transcranial magnetic stimulation (TMS) was used to investigate the causal involvement of frontal and parietal areas in different stages of the PM process (in particular, target checking and intention retrieval), and to determine the specific contribution of these regions to PM performance. Our results demonstrate that repetitive TMS (rTMS) interferes with prospective memory performance when applied at 150-350 ms to the right dorsolateral prefrontal cortex (DLPFC), and at 400-600 ms when applied to the left posterior parietal cortex (PPC). The present study provides clear evidence that the right DLPFC plays a crucial role in early components of the PM process (target checking), while the left PPC seems to be mainly involved in later processes, such as the retrieval of the intended action.

Planning times during traveling salesman's problem: differences between closed head injury and normal subjects.

We studied planning behavior in a group of normal subjects and a group of closed head injury patients (CHI). A computerized version of the traveling salesman's problem was used as a visuospatial planning ability task. The program collected measurements of partial times, number of moves, and number of skipped subgoals. These measures allow us to calculate a "planning index" of subjects' planning ability. Results show that CHI patients present limitations in the planning process due to the lack of ongoing planning.

Neuropsychological evaluation of neurologically asymptomatic HIV-infected children.

Forty-two children born to HIV positive mothers (29 infected at different stages of the disease, according to the Disease Control Classification Centers, and 13 noninfected) underwent evaluation using a battery of neuropsychological tests. Executive function impairments were present in all infected children, whereas memory and visuo-prassic deficits were evident only in those with full-blown AIDS. Language abilities and overall intelligence were spared. Performance of seroreverters was in the normal range. These findings suggest that even in neurologically asymptomatic children, neuropsychological evaluation can identify early impairment of specific cognitive functions. The findings are discussed in the light of the prognostic power of neuropsychological assessment for early signs of HIV neurological involvement.

Tacit integration and referential structure in the language comprehension of aphasics and normals.

Aphasics, brain-damaged patients with no language deficit, neurologically intact elderly subjects, and university undergraduates matched pictures to sentences having compelling tacit implications (e.g., the sentence The fox grabs the hen strongly invites one to assume that the fox will eat the hen). All groups made, for the same sentences, qualitatively similar referential errors consisting in choosing a tacit implication picture. Two auxiliary experiments using the same target sentences in other interpretive situations permitted ruling out the possibility that these errors were due to the putative intrinsic semantic properties of the sentences, showing that the sentences which were most liable to elicit integrative error varied from task to task. These results are interpreted within the conceptual framework which posits that reliable directions for interpretation are couched by the speaker in the very structure of his utterances (the utterance's referential structure) providing the hearer with means to restructure the relevant personal knowledge integrated into the interpretive process in accordance with the speaker's communicative intent. The determination of the referential structure (RSD) of utterances thus seems critical to their correct or, more precisely, conventional interpretation, and, along with the tacit integration of relevant sources of personal knowledge, constitutes the principal cognitive device enabling us to understand each other. But this device appears to be easily corruptible. It is suggested that many errors made by aphasics in language interpretation are due to a failure to follow all referential instructions, but that qualitatively similar failures also occur in normal subjects, though to a lessen degree. Language interpretation is a fallible process and aphasic errors provide remarkable clues for the understanding of its subtle referential mechanisms.

Left-right asymmetry of callosal transfer in normal human subjects.

Interhemispheric transfer (IT) of visuomotor information can be assessed by measuring the crossed-uncrossed difference (CUD) in the Poffenberger paradigm [14]. We report a series of experiments aimed at casting light on two aspects of IT: the importance of motor response variables and the nature of the left-right asymmetries found in a recent meta-analysis of studies using the Poffenberger paradigm [10]. In Experiments 1 and 2 we found no effect of varying the finger used for response while there was a larger CUD when using the left hand in comparison to the right hand. In Experiment 3, which employed visual stimuli different from the two preceding experiments, CUD asymmetries were related to hemifields rather than to hands with a CUD larger for the right than for the left visual hemifield. These findings suggests that both motor and visual variables are important for CUD asymmetries to occur and are in keeping with a horse race model according to which overall speed of IT is determined by whichever signal (visual or pre-motor) is more rapid in crossing from one side to the other. As to the issue of lateral asymmetries in the CUD, the results of Expt. 3 have also shown that asymmetries arise only in tasks requiring an IT and therefore cannot depend upon additive hemispheric effects.

Naming disorders and semantic representations.

The status of semantic conceptual structures in aphasia was investigated with relation to naming disorders in spontaneous and constrained speech production. A battery of six tasks was administered to 25 control subjects and 25 aphasics: spontaneous speech production (from which the percentage of nouns was calculated), confrontation naming, understanding class relationships (verbal and pictorial), and understanding thematic relationships (verbal and pictorial). Results indicated the important role of taxonomic abilities for naming, while other conceptual structures (i.e., thematic relations) do not seem to play any important role in the process of naming. These results are discussed in terms of the internal organization of semantic information.

Spatial sustained attention: better focused than divided?

Visuospatial attention was studied using three different reaction time tasks in a sustained attention paradigm (N = 35). Contrasting with findings from a phasic attention paradigm, our results suggest an equal ability to divide or focus sustained attention in the left and right fields in simple RT, a Go/No go-task, and choice RT.

Is interhemispheric transfer of visuomotor information asymmetric? Evidence from a meta-analysis.

Using a meta-analytic procedure we have analysed 16 studies employing a simple unimanual reaction time (RT) paradigm and lateralized visual stimuli to provide an estimate of interhemispheric transfer time in normal right-handed subjects. We found a significant overall RT advantage of the left visual field over the right and of the right hand over the left. These asymmetries can be explained by a superiority of the right hemisphere for the detection of simple visual stimuli and by a corresponding superiority of the left hemisphere for the execution of the manual response, respectively. Alternatively, they may be interpreted as related to an asymmetry of interhemispheric transmission of visuomotor information, with transfer from the right hemisphere (side of stimulus entry) to the left (side of response generation) faster than in the reverse direction. Although a direct test of these hypotheses is still lacking, we think that the evidence available is more in keeping with the latter possibility.

Unimanual tapping during concurrent articulation: examining the role of cortical structures in the execution of programmed movement sequences.

Three experiments were conducted to examine effects of speech on concurrent unimanual tapping. Experiments 1 and 2 involved the manual tapping of a short burst of preprogrammed responses with or without concurrent articulation. Results of these experiments showed no effects of speech articulation on the concurrent execution of programmed manual movement sequences. In Experiment 3, subjects continuously tapped for 15 sec, again, with or without concurrent speech articulation. The results showed that articulation affected the speed of concurrent manual responses with larger interference for right hand tapping than for left hand tapping. Additional analysis of the tapping variability revealed equivalent effects of concurrent articulation on the timing of repetitive right and left hand tapping. Kinsbourne's Functional Cerebral Distance Principle was used to interpret these results. Within this framework, the present findings indicate that functionally distinct processes control speech articulation and the execution of programmed manual movement sequences.

Impairment in processing meaningless verbal material in several modalities: the relationship between short-term memory and phonological skills.

Phonological processing abilities were studied in a patient who, following focal brain damage, showed selective impairment in non-word reading, writing, and repetition and also a severe short-term memory (STM) deficit specific for auditorily presented verbal material. The patient could execute tasks involving phonemic manipulation and awareness perfectly. Our data, in contrast with earlier observations in a case of developmental phonological dyslexia, show that acquired impairment in non-word reading, writing, repetition, and immediate memory may occur despite good phonological processing abilities. The role of STM in processing meaningless verbal material is discussed.

Left hemisphere superiority for visuospatial functions in left-handers.

Male and female left- and right-handers have been tested with a divided visual field technique on a visuospatial (discrimination of angle width) and on a verbal task (vowel-consonant discrimination) using either a choice or a Go-No-go manual reaction time paradigm. Right-handers showed the expected pattern of hemispheric asymmetries with an advantage of the right hemisphere in the visuospatial task and an advantage of the left hemisphere in the verbal task. Such effects were statistically reliable only in male subjects. Left-handers, on the contrary, showed a different pattern of asymmetries. In the visuospatial task there was an overall superiority of the left hemisphere, while no hemispheric asymmetry was found in the verbal task.

Acquired stuttering: a motor programming disorder?

Acquired stuttering (AS) can follow unilateral right, left or bilateral hemispheric lesion, and can, but not necessarily, coexist with aphasia. In this paper we experimentally tested motor programming skills in a patient with AS of vascular origin. Motor programming consists in the structuration of the whole sequence of response prior to the onset of the first response element of a sequence of responses. Chronometric studies have shown that the time to initiate a sequence of manual responses is a function of the characteristics of the forthcoming sequence of responses. In our patient, reaction times involving single motor responses performed by right hand were within normal limit. On the contrary, when the task required a sequence of motor responses, there was a consistent difficulty in following the sequence: moreover, in the few correct sequences, reaction time analysis showed a lack of motor programming. It is suggested that AS could be the speech epiphenomenon of a more generalized disturbance of motor programming.

Successful and unsuccessful strategies of search in auditory memory.

In a multiple-target single-probe experiment on auditory memory, evidence was obtained for two different strategies off search, one being more efficient than the other both in terms of accuracy and rapidity. The result urges us to be cautious in the interpretation of experiments in which a large number of subjects low in accuracy are discarded in the screening phase.