Biomedical subjects

P Walla

Publications and source records attributed to P Walla.

At least 19 recordsLinked to original sources

PubMed2006

Sensory-specific satiety with simple foods in humans: no influence of BMI?

OBJECTIVE: Olfacto-gustatory sensory-specific satiety plays an important role in the termination of food ingestion. A defect in this mechanism, by increasing food intake, could be a factor in development of overweight. The present study was conducted to explore whether sensory-specific satiety in the overweight may be different from that in normal-weight subjects. SUBJECTS: 144 subjects (half men, half women; age range: 17-62 years; BMI range: 17-39 kg m(-2)). MEASUREMENTS: Olfactory pleasure (OP) and flavor pleasure (FP) were evaluated before and after ingestion of a single chosen food. Six foods from three classes were offered: cucumber and tomato, pineapple and banana, and peanut and pistachio. According to the subjects' preference for one of them, subjects were classified into six groups (24 subjects each with equal sex ratio). The experimental sequence was (1) evaluation of the six foods (OP), (2) ad libitum intake of the preferred food (FP) and (3) second evaluation of the six foods (OP). RESULTS: Food intake was limited by sensory-specific satiety (that is, a decline in FP for the ingested food) in overweight subjects just as it was in the leanest. There was no significant correlation between BMI and hedonic parameters (OP and FP) or intakes (quantity and volume). Pre-ingestive OP and FP correlated with the ingested food's weight (OP: r=0.468; FP: r=0.415; P<0.01), volume (OP: r=0.428; FP: r=0.407; P<0.01) and intake duration (OP: r=0.184; FP: r=0.343; P<0.05). The decline in OP, but not in FP, correlated with ingested weight (r=0.271, P<0.01) and volume (r=0.263, P<0.01) but not with duration. CONCLUSION: After intake of a single food, olfacto-gustatory sensory-specific satiety correlated with the ingested food's weight and volume and with the duration of ingestion, but not with bodyweight. This suggests that overweight and lean subjects have similar hedonic control of food intake with simple foods.

Adolescent↗

PubMed2006

EEG evidence of gender differences in a motor related CNV study.

In the present study gender differences related to the contingent negative variation (CNV) were investigated. A series of two acoustic stimuli was presented to participants across a wide age range. The first stimulus was consistent throughout the experiment whereas the second one was either a high frequency or a low frequency tone. One of them had to be answered by a button press (go condition) the other did not require any response (nogo condition). Between the first and the second tone there was a time period of two seconds in which the CNV appeared as a slow negative potential shift. Within this episode data were analysed with respect to gender differences. Statistical analysis revealed topographical differences between men and women in go conditions for both left and right index finger movements. Differences were found over frontal regions where women showed higher brain activity than men and over temporo-parietal regions where men produced higher brain activity than women. In order to explain the fact that only in "go" conditions significant gender differences occurred we introduce the phenomenon of implicit learning. Due to implicit learning assumed predictions related to S2 might have occurred from time to time. This is so, because a 50% chance for one of two different stimuli to occur leads to reasonable assumed predictions after two or more stimuli of a kind occurring in a series. The present data now provide evidence that if such assumed prediction or expectancy is directed towards an upcoming demand to act then brain activity is subject to gender differences. Further studies providing controlled sequences of "go" conditions versus "nogo" conditions have to be done to prove this idea true.

Acoustic Stimulation↗

PubMed2005

Magnetoencephalographic correlates of different levels in subjective recognition memory.

In our current study we employed whole-head magnetoencephalography (MEG) to identify neurophysiological correlates (event-related fields, ERFs) of different phenomenologies in human recognition memory. Words which had previously been semantically processed were presented along with previously unstudied words. Via button presses, participants provided subjective indices of three forms of memory: confident recognition, familiarity-based recognition, and misclassification of previously presented items as new (no recognition, misses). Behavioral results revealed a clear distinction between confident recognition (shortest reaction times) and familiarity-based recognition and misses, respectively, and physiological data pointed to bilateral anterior and left anterior/central regions in which magnetic field patterns were directly related to word recognition from approximately 300 ms to 500 ms after word onset. In the context of the prevalent dual process controversy on the roles of familiarity and recollection in recognition memory, we first highlight that two operationalizations of recollection need to be differentiated: We argue that a strategic search for a particular contextual feature stands in clear contrast to the fast and incidental availability of some contextual feature and derive experimental and behavioral indicators for either form of recollection. These indicators are used to select from manifold cognitive neuroscientific work on recognition memory in order to further discuss the neurocognitive characteristics of incidental recollection in contrast to other forms of episodic memory.

Adult↗

PubMed2005

Neurocognitive correlates of incidental verbal memory encoding: a magnetoencephalographic (MEG) study.

In our current study, we applied whole head magnetoencephalography (MEG) in a subsequent memory paradigm. Magnetic fields were recorded while 20 healthy subjects (10 females, 10 males) incidentally encoded words during semantic and structural verbal processing tasks. Physiological data were then sorted according to the performance in subsequent memory tests and according to levels of processing, respectively, and analyzed for gender effects. Behavioral results show a clear advantage of semantic processing over structural processing with respect to retrieval success for both females and males. Despite alikeness of behavioral data, MEG results show considerable differences between males and females concerning both subsequent memory effects and levels of processing effects. For male subjects, we identified more distinct magnetic fields in anterior regions for subsequently remembered than for subsequently forgotten words (latency range from 300-650 ms after word onset) and for semantic processing than for structural processing, respectively. For female subjects, corresponding magnetic field differences pointed to posterior regions (subsequent memory effects from 450 ms to 750 ms after word onset). No qualitative differences were observed between subsequent memory effects during semantic processing compared to subsequent memory effects during structural processing. We try to reconcile results from male data with previous findings concerning subsequent memory effects by proposing the concept of width of processing, which holds that incidental memory formation is mediated by frontal activity on a physiological level and brought forward on a cognitive level by enhanced associating imposed by the task demands of semantic processing. Female data cannot be fully incorporated in this framework, but all the more prompt further gender-specific analyses of subsequent memory effects.

Adult↗

PubMed2004

Depth of word processing in Alzheimer patients and normal controls: a magnetoencephalographic (MEG) study.

Effects related to depth of verbal information processing were investigated in probable Alzheimer's disease patients (AD) and age matched controls. During word encoding sessions 10 patients and 10 controls had either to decide whether the letter "s" appeared in visually presented words (alphabetical decision, shallow encoding), or whether the meaning of each presented word was animate or inanimate (lexical decision, deep encoding). These encoding sessions were followed by test sessions during which all previously encoded words were presented again together with the same number of new words. The task was then to discriminate between repeated and new words. Magnetic field changes related to brain activity were recorded with a whole cortex MEG.5 probable AD patients showed recognition performances above chance level related to both depths of information processing. Those patients and 5 age matched controls were then further analysed. Recognition performance was poorer in probable AD patients compared to controls for both levels of processing. However, in both groups deep encoding led to a higher recognition performance than shallow encoding. We therefore conclude that the performance reduction in the patient group was independent of depth of processing. Reaction times related to false alarms differed between patients and controls after deep encoding which perhaps could already be used for supporting an early diagnosis. The analysis of the physiological data revealed significant differences between correctly recognised repetitions and correctly classified new words (old/new-effect) in the control group which were missing in the patient group after deep encoding. The lack of such an effect in the patient group is interpreted as being due to the respective neuropathology related to probable AD. The present results demonstrate that magnetic field recordings represent a useful tool to physiologically distinguish between probable AD and age matched controls.

Aged↗

PubMed2003

Preserved memory traces within diencephalic amnesia.

A male patient with bilateral thalamic lesions (medio-ventral nuclei) was investigated. Despite explicit memory impairments his lexical ability was normal. We recorded magnetic field changes (magnetoencephalography, MEG) during the performance of an animate/inanimate discrimination task in which some words where repeated after long delays. Normally, repeated items are classified significantly faster than their first presentations which is accomplished by an unconscious process called priming. The patient did not show any behavioural evidence of priming but the physiological data indicated preservation of this robust form of memory. Brain activation associated with repetitions was attenuated at early stages. The activity difference was posteriorly distributed which is consistent with previous reports about repetition priming. The present study indicated that the bilateral thalamic lesions of our patient disconnected the information processing stream between the primed information and the behavioural response.

Amnesia↗

PubMed2003

Magnetoencephalographic--features related to mild cognitive impairment.

We recorded changes of brain activity from 10 MCI patients and 10 controls related to shallow (nonsemantic) and deep (semantic) word encoding using a whole-head MEG. During the following recognition tasks, all participants had to recognize the previously encoded words, which were presented again together with new words. In both groups recognition performance significantly varied as a function of depth of processing. No significant differences were found between the groups. Reaction times related to correctly classified new words (correct rejections) and incorrectly classified repetitions (misses) of MCI patients showed a strong tendency toward prolongation compared to controls, although no statistically significant differences occurred. Strikingly, in patients the neurophysiological data associated with nonsemantic and semantic word encoding differed significantly between 250 and 450 ms after stimulus onset mainly over left frontal and left temporal sensors. They showed higher electrophysiological activation during shallow encoding as compared to deep encoding. No such significant differences were found in controls. The present results might reflect a dysfunction with respect to shallow encoding of visually presented verbal information. It is interpreted that additional neural activation is needed to compensate for neurodegeneration. This finding is suggested to be an additional tool for MCI diagnosis.

Aged↗

PubMed2001

Left temporal and temporoparietal brain activity depends on depth of word encoding: a magnetoencephalographic study in healthy young subjects.

Using a 143-channel whole-head magnetoencephalograph (MEG) we recorded the temporal changes of brain activity from 26 healthy young subjects (14 females) related to shallow perceptual and deep semantic word encoding. During subsequent recognition tests, the subjects had to recognize the previously encoded words which were interspersed with new words. The resulting mean memory performances across all subjects clearly mirrored the different levels of encoding. The grand averaged event-related fields (ERFs) associated with perceptual and semantic word encoding differed significantly between 200 and 550 ms after stimulus onset mainly over left superior temporal and left superior parietal sensors. Semantic encoding elicited higher brain activity than perceptual encoding. Source localization procedures revealed that neural populations of the left temporal and temporoparietal brain areas showed different activity strengths across the whole group of subjects depending on depth of word encoding. We suggest that the higher brain activity associated with deep encoding as compared to shallow encoding was due to the involvement of more neural systems during the processing of visually presented words. Deep encoding required more energy than shallow encoding but for all that led to a better memory performance.

Adult↗

PubMed2001

False recognition depends on depth of prior word processing: a magnetoencephalographic (MEG) study.

Brain activity was measured with a whole head magnetoencephalograph (MEG) during the test phases of word recognition experiments. Healthy young subjects had to discriminate between previously presented and new words. During prior study phases two different levels of word processing were provided according to two different kinds of instructions (shallow and deep encoding). Event-related fields (ERFs) associated with falsely recognized words (false alarms) were found to depend on the depth of processing during the prior study phase. False alarms elicited higher brain activity (as reflected by dipole strength) in case of prior deep encoding as compared to shallow encoding between 300 and 500 ms after stimulus onset at temporal brain areas. Between 500 and 700 ms we found evidence for differences in the involvement of neural structures related to both conditions of false alarms. Furthermore, the number of false alarms was found to depend on depth of processing. Shallow encoding led to a higher number of false alarms than deep encoding. All data are discussed as strong support for the ideas that a certain level of word processing is performed by a distinct set of neural systems and that the same neural systems which encode information are reactivated during the retrieval.

Adult↗

PubMed2001

Physiological evidence of gender differences in word recognition: a magnetoencephalographic (MEG) study.

Magnetic field recordings were made in order to describe brain processes during a word recognition experiment. We investigated 26 healthy young subjects (14 females) and focused on gender differences related to recognition performance and brain activity. From about 200 ms to 350 ms after word onset the event-related field (ERF) patterns differed significantly between women and men, although the mean recognition performances did not. Differences were due to different strengths of activation as well as due to the involvement of different neural structures as underlined with statistical analysis. We interpret that our physiological findings demonstrate that different mental strategies are used for correct word recognition in the brains of women and men as assessed with magnetoencephalography (MEG). Our data might be linked to previous findings about the hemispheric asymmetry in male subjects (left lateralized) compared to women in whom both hemispheres seem to be equally involved in word processing.

Adult↗

PubMed2001

A medial to lateral shift in pre-movement cortical activity in hemi-Parkinson's disease.

OBJECTIVE: Recent evidence suggests that cortical activity associated with voluntary movement is relatively shifted from medial to lateral premotor areas in Parkinson's disease. This shift occurs bilaterally even for unilateral responses. It is not clear whether the shift in processing reflects an overall change in movement strategy, thereby involving alternate cortical areas, or reflects a compensatory change whereby, given the appropriate conditions, less impaired cortical areas are able to provide a similar function in compensation for those areas which are more impaired. This issue was examined in patients with hemi-Parkinson's disease, in whom basal ganglia impairment is most pronounced in one hemisphere. METHODS: Fourteen patients with hemi-Parkinson's disease and 15 age-matched control subjects performed a Go/NoGo finger movement task and the contingent negative variation (CNV) was recorded from 21 scalp positions. RESULTS AND CONCLUSIONS: Maximal CNV amplitudes were found over central medial regions for control subjects, but were shifted more frontally for Parkinson's disease patients, reduced in amplitude over the midline and lateralized towards the side ipsilateral to the greatest basal ganglia impairment. This shift in cortical activity from medial to lateral areas in Parkinson's disease patients appears to reflect a compensatory mechanism operating predominantly on the side of greatest basal ganglia impairment.

Action Potentials↗

PubMed2000

False recognition in a verbal memory task: an event-related potential study.

Brain potentials were recorded from 15 healthy young subjects during the performance of a word recognition task. During the study phase, subjects had to intentionally memorise a series of words. These words were presented again together with the same number of new words in a following test phase where the instruction was to discriminate between repeated words and new words. We compared event-related potentials (ERPs) evoked by correctly identified repeated words (hits) and ERPs evoked by incorrectly classified new words (false alarms). Although both types of words were thought to be repeated the ERPs indicated differences between these two conditions starting at about 450 ms after the stimulus onset. These differences were mostly pronounced over frontal scalp locations but occurred also over parietal scalp locations (false alarms produced significantly more negative going ERPs than hits). We interpret that frontal and parietal brain areas show greater activation during false recognition because of a more intensive search for item representations.

Adult↗

PubMed1999

Different forms of human odor memory: a developmental study.

Recognizing odors is an important biological function, both in the animal kingdom as well as for humans. It has been debated whether there exist different forms of human odor memory. For verbal memory, the concept of recollection and familiarity for conscious and unconscious recognition is widely accepted. Here we introduce a similar model for human odor memory. We use a combination of an odor naming and odor recognition memory task to estimate the relationship between depth of processing and retention of olfactory information. A developmental approach with children, young adults, middle aged adults and elderly subjects was chosen in order to study the influence of age. Our results indicate the existence of two separable forms of odor memory depending on whether the odors were correctly or incorrectly named during the naming task. These two forms of odor memory were differently represented across the human age range. Intact familiarity-based memory was found in all age groups, whereas memory based on recollection was impaired in the elderly and not yet fully developed in children. Our data show, for the first time, two different forms of human odor memory across the human life span.

Adolescent↗

PubMed1999

Implicit memory within a word recognition task: an event-related potential study in human subjects.

First, we recorded brain potentials from 15 healthy young subjects during the performance of a word/non-word discrimination task. During continuous visual presentation, some of the meaningful words were repeated after 86-94 s. We found a significant decrease of response time associated with the classification of repeated words which is an index for priming, an unconscious brain process. However, event-related potentials (ERPs) did not differ significantly between first and second presentations. Second, we recorded brain potentials during a following recognition test. Some of the meaningful words which were presented only once during the semantic discrimination task were repeated and had to be discriminated from randomly interspersed new words. We compared ERPs produced by incorrectly classified repeated words (misses) with ERPs produced by correctly classified new words (correct rejections). We found early ERP differences between 250 and 400 ms and later differences starting at about 500 ms after the stimulus onset. The early effect occurred over parietal scalp locations and the later effect over frontal, parietal and occipital scalp locations. This is evidence for unconscious brain activity related to the processing of missed repeated words. We suggest that the later frontal effect we found is due to an enhanced effort of the retrieval of item representations during word recognition and that the earlier parietal effect reflects partial recognition.

Adult↗

PubMed1999

Event-related potential correlates of false recognitions of faces.

In a recognition memory experiment we recorded event-related brain potentials (ERPs) following the presentation of faces. We compared correctly classified repetitions of faces (hits) with new faces classified as repeated (false alarms). Stimulus-related averaging yielded significantly more negative ERPs to false alarms between 750 and 900 ms after onset of stimulus presentation. With response-related averaging we found significantly more negative ERPs to false alarms within the last 100 ms before movement onset. The differential activity was distributed over central and frontal regions and was still present in the period after the response. We interpret the phenomenon as an electrophysiological manifestation of false recognition as described by Schacter et al. (Schacter, D.L., Norman, K.A. and Koutstaal, W., The cognitive neuroscience of constructive memory, Annu. Rev. Psychol., 49 (1998) 289-318). False recognition could be the result of a preliminary decision based on illusionary familiarity and be associated with post-retrieval processing.

Evoked Potentials↗

PubMed1999

Early occipito-parietal activity in a word recognition task: an EEG and MEG study.

OBJECTIVE: We investigated early brain activity (under 200 ms after the stimulus onset) related to the encoding and the retrieval of verbal information. METHODS: First, we compared ERPs produced by words which were encoded to ERPs produced by words from following test phases (correctly identified repetitions and correctly classified new words) in two different experiments. Experiment 1 consisted of an intentional learning paradigm and experiment 2 consisted of an incidental learning paradigm. In addition, we conducted a control experiment (experiment 3), which was a continuous recognition task with two different repetition intervals. Secondly, we conducted a magnetoencephalographic (MEG) study to further investigate early brain activity (experiment 4). The same intentional learning paradigm as in experiment 1 was used. RESULTS: We found that ERPs elicited by correctly classified test words (repeated words and new words) of both experiment 1 and experiment 2 were significantly more negative going than the ERPs elicited by the study words. This effect was apparent between 100 ms and 200 ms after the stimulus onset and was distributed over occipital and parietal scalp locations. In the control task (experiment 3), these early potential differences were missing (for both repetition intervals). Early event-related fields (ERFs) were also found to depend on the situation of the study phase and the test phase. This activity difference peaked at 120 ms after the stimulus onset. The distributions of the difference magnetic fields were occipito-parietal and thus consistent with the findings of experiment 1 (EEG-experiment). CONCLUSION: Whether the effect we defined in the present study is due to an increase of activity during the test situation or due to a decrease of activity during the study situation remains unclear. However, it might reflect attentional processes within a word recognition task depending on whether a word is encoded or an effort of word retrieval has to be made.

Adult↗

PubMed1998

Dissociation of the neural correlates of implicit and explicit memory.

One presentation of a word to a subject is enough to change the way in which the word is processed subsequently, even when there is no conscious (explicit) memory of the original presentation. This phenomenon is known as implicit memory. The neural correlates of implicit memory have been studied previously, but they have never been compared with the correlates of explicit memory while holding task conditions constant or while using a procedure that ensured that the neural correlates were not 'contaminated' by explicit memory. Here we use scalp-recorded event-related brain potentials to identify neural activity associated with implicit and explicit memory during the performance of a recognition memory task. Relative to new words, recently studied words produced activity in three neuroanatomically and functionally dissociable neural populations. One of these populations was activated whether or not the word was consciously recognized, and its activity therefore represents a neural correlate of implicit memory. Thus, when task and memory contamination effects are eliminated, the neural correlates of explicit and implicit memory differ qualitatively.

Adult↗

PubMed1998

Early cortical activation indicates preparation for retrieval of memory for faces: an event-related potential study.

Event-related brain potentials (ERPs) were used to investigate the time course of memory processes following the presentation of faces. Following a phase in which subjects were asked to memorize faces presented on a computer screen (study phase) they had to distinguish the previously presented faces from others new to the experiment (test phase). We found that in a time period from 250 to 350 ms after onset of stimulus presentation ERPs show higher negativity for both repeated and novel faces in the test phase compared to the study phase. This situation dependent effect is most pronounced in occipito-temporal regions. We conclude that memory retrieval for faces is a sequential process. The early part of this process constitutes preparation for the retrieval of stored information, and a later part of the process comprises the discrimination between repeated and novel faces.

Adult↗