Olivier Koenig

Emotional Responses to Pleasant and Unpleasant Olfactory, Visual, and Auditory Stimuli: a Positron Emission Tomography Study

Neural correlates of responses to emotionally valenced olfactory, visual, and auditory stimuli were examined using positron emission tomography. Twelve volunteers were scanned using the water bolus method. For each sensory modality, regional cerebral blood flow (rCBF) during presentation of both pleasant and unpleasant stimuli was compared with that measured during presentation of neutral stimuli. During the emotionally valenced conditions, subjects performed forced-choice pleasant and unpleasant judgments. During the neutral conditions, subjects were asked to select at random one of a two key-press buttons. All stimulations were synchronized with inspiration, using an airflow olfactometer, to present the same number of stimuli for each sensory modality. A no-stimulation control condition was also performed in which no stimulus was presented. For all three sensory modalities, emotionally valenced stimuli led to increased rCBF in the orbitofrontal cortex, the temporal pole, and the superior frontal gyrus, in the left hemisphere. Emotionally valenced olfactory and visual but not auditory stimuli produced additional rCBF increases in the hypothalamus and the subcallosal gyrus. Only emotionally valenced olfactory stimuli induced bilateral rCBF increases in the amygdala. These findings suggest that pleasant and unpleasant emotional judgments recruit the same core network in the left hemisphere, regardless of the sensory modality. This core network is activated in addition to a number of circuits that are specific to individual sensory modalities. Finally, the data suggest a superior potency of emotionally valenced olfactory over visual and auditory stimuli in activating the amygdala.

Functional Anatomy of Perceptual and Semantic Processing for Odors

The functional anatomy of perceptual and semantic processings for odors was studied using positron emission tomography (PET). The first experiment was a pretest in which 71 normal subjects were asked to rate 185 odorants in terms of intensity, familiarity, hedonicity, and comestibility and to name the odorants. This pretest was necessary to select the most appropriate stimuli for the different cognitive tasks of the second experiment. The second one was a PET experiment in which 15 normal subjects were scanned using the water bolus method to measure regional cerebral blood flow (rCBF) during the performance in three conditions. In the first (perceptual) condition, subjects were asked to judge whether an odor was familiar or not. In the second (semantic) condition, subjects had to decide whether an odor corresponded to a comestible item or not. In the third (detection) condition, subjects had to judge whether the perceived stimulus was made of an odor or was just air. It was hypothetized that the three tasks were hierarchically organized from a superficial detection level to a deep semantic level. Odorants were presented with an air-flow olfactometer, which allowed the stimulations to be synchronized with breathing. Subtraction of activation images obtained between familiarity and control judgments revealed that familiarity judgments were mainly associated with the activity of the right orbito-frontal area, the subcallosal gyrus, the left inferior frontal gyrus, the left superior frontal gyrus, and the anterior cingulate (Brodmanns areas 11, 25, 47, 9, and 32, respectively). The comestibility minus familiarity comparison showed that comestibility judgments selectively activated the primary visual areas. In contrast, a decrease in rCBF was observed in these same visual areas for familiarity judgments and in the orbitofrontal area for comestibility judgments. These results suggest that orbito-frontal and visual regions interact in odor processing in a complementary way, depending on the task requirements.

Separable mechanisms in face processing: Evidence from hemispheric specialization

This article addresses three issues in face processing: First, is face processing primarily accomplished by the right hemisphere, or do both left- and right-hemisphere mechanisms play important roles? Second, are the mechanisms the same as those involved in general visual processing, or are they dedicated to face processing? Third, how can the mechanisms be characterized more precisely in terms of processes such as visual parsing? We explored these issues using the divided visual field methodology in four experiments. Experiments 1 and 2 provided evidence that both left- and right-hemisphere mechanisms are involved in face processing. In Experiment 1, a right-hemisphere advantage was found for both Same and Different trials when Same faces were identical and Different faces differed on all three internal facial features. Experiment 2 replicated the right-hemisphere advantage for Same trials but showed a left-hemisphere advantage for Different trials when one of three facial features differed between the target and the probe faces. Experiment 3 showed that the right-hemisphere advantage obtained with upright faces in Experiment 2 disappeared when the faces were inverted. This result suggests that there are right-hemisphere mechanisms specialized for processing upright faces, although it could not be determined whether these mechanisms are completely face-specific. Experiment 3 also provided evidence that the left-hemisphere mechanisms utilized in face processing tasks are general-purpose visual mechanisms not restricted to particular classes of visual stimuli. In Experiment 4, a left-hemisphere advantage was obtained when the task was to find one facial feature that was the same between the target and the probe faces. We suggest that left-hemisphere advantages shown in face processing are due to the parsing and analysis of the local elements of a face.

Categorical and coordinate spatial relations : fMRI evidence for hemispheric specialization

Functional magnetic resonance imaging (fMRI) was applied to determine the involvement of the angular gyri in the processing of categorical and coordinate spatial relations. In a categorical task, subjects were asked to judge whether a dot was presented above or below a horizontal line. In a coordinate task, they were asked to judge whether or not the distance between the dot and the bar was within a reference distance. Results showed stronger activation of the left than of the right angular gyrus in the categorical task, and stronger activation, initially, of the right than of the left angular gyrus in the coordinate task. In addition, in the latter task, the involvement of the right angular gyrus decreased with practice while that of the left angular gyrus increased. These results are interpreted in terms of the development of new categorical representations with practice in the coordinate task.

The development of spatial relation representations: evidence from studies of cerebral lateralization.

Twenty-four-5-year-olds and 24 7-year-olds completed two divided-visual-field tasks; one task required subjects to categorize a dot as above or below a line, whereas the other required subjects to determine whether the dot was within 3 mm of the line. There was a relative left-hemisphere advantage for the above/below task and a relative right-hemisphere advantage for the distance task. The results indicate that distinct processing subsystems compute different kinds of visuo-spatial relations as early as 5 years of age.

Evidence for different types of lexical representations in the cerebral hemispheres

Abstract Forty right-handed, neurologically intact adults performed a lexical decision task with stimuli presented to the left visual field (right hemisphere) or to the right visual field (left hemisphere). Nonwords, low-frequency words, and high-frequency words were used as stimuli. Although an overall lefthemisphere advantage was observed for words, lateral differences did not differ according to word frequency. The results revealed further that when morphologically decomposable nonwords consisting of inappropriately combined legal stem plus suffix were presented in the right visual field they engendered more errors than matched nonwords that could not be parsed into stem plus suffix. In contrast, morphologically decomposable and nondecomposable nonwords engendered identical performance when stimuli were presented in the left visual field. These results were interpreted as suggesting that morphologically decomposed forms are only represented in the left hemisphere.

Procedural learning in Parkinson’s disease: Intact and impaired cognitive components

Two experiments were carried out to study procedural learning in Parkinsons disease (PD) patients. In Experiment 1, ten patients and their normal controls participated in a classical mirror reading task and in an inverted reading task where word-stimuli made of non inverted letters had to be processed from right to left (e.g., ygoloruen). In both tasks, reading times for new stimuli were compared to reading times for stimuli that repeated over blocks. Although PD patients and their controls exhibited learning for repeated words in both tasks, PD patients did not respond faster with practice for new words in the inverted reading task. In Experiment 2, PD patients and their controls were presented with an original dot counting task in which participants were asked to process a horizontal series of black and white dots from right to left and to indicate whether a dot that had been designated by a number at the beginning of each trial was black or white. Results showed that PD patients, in contrast to controls, did not exhibit learning in this task. Results are discussed in terms of the cognitive components involved in these tasks. It is suggested that PD patients are impaired in the acquisition of a right-to-left visual scanning skill that could be studied directly in Experiment 2.

On the relationship between visual imagery and visual perception: Evidence from priming studies

Two priming experiments using a perceptual identification task were conducted to explore the functional and representational overlap between visual imagery and visual perception. The first experiment included a study phase in which primes were either perceived or imaged objects and a perceptual identification test task in which targets were parts of studied and non-studied objects. Imagery primed identification when subjects were instructed to count the parts of the imaged objects in the study phase but not when they were instructed to focus on the global shape of the imaged objects. This result suggests that imagery involves perceptual representations identical to those involved in perception. It also suggests that the representational overlap between imagery and perception depends on the type of images generated, as some images may consist in global shapes only, whereas others may consist in detailed, multi-part shapes. In the second experiment, we used whole objects as target stimuli which provided subjects with more information to identify masked targets and thereby reduced top-down processing. Priming from imagery fell beneath significance, suggesting that this sort of priming is elicited in a large part by a transfer of top-down processes from study to test.

Midazolam effects on implicit and explicit memory processes in healthy subjects.

Abstract Rationale: Studying midazolam-induced amnesia offers an interesting approach to the organization of normal memory processes, since memory performance can be studied in the same subject in ”on” and ”off” drug conditions. Objective: The present study investigated the effect of midazolam on skill learning. The task and the experimental design we used also allowed us to assess the effect of midazolam on priming and explicit memory. Methods: Eighteen patients who underwent minor ear surgery and who were anaesthetized with intravenous midazolam, and 18 matched control subjects participated in a mirror reading task on 2 separate days. Patients were tested under midazolam on day 1 and without any medication on day 2. The mirror reading task was made of French words, some of which repeated across trial blocks, others being new. Results: Patients under midazolam read new mirror written words faster with practice, which attested for intact skill learning. Moreover, they read repeated words faster than new words with practice, which was interpreted as reflecting intact priming abilities. These spared implicit memory capacities were observed along with severe explicit memory impairments. Learning for both new and repeated mirror written words on day 2 was similar in patients and in controls, which was interpreted as suggesting that the implicit learning that occurred on day 1 under midazolam was normal. Conclusions: The quality of skill learning, both in terms of speed of and lasting effect, was normal under midazolam in the task we used. In the context of the present task, midazolam offers an interesting, reversible model of amnesia.

Optimising retention through multiple study opportunities over days: The benefit of an expanding schedule of repetitions

Few studies have investigated how scheduling repeated studies of the same material over several days influences its subsequent retention. The study-phase retrieval hypothesis predicts that, under these circumstances, expanding intervals between repetitions will promote the greatest likelihood that the participant will be reminded of previous occurrences of the item, thus leading to a benefit for subsequent recall. In the present article, participants studied vocabulary pairs that were repeated according to one of three schedules. In the expanding schedule, pairs were presented on days 1, 2 and 13; in the uniform schedule, on days 1, 7 and 13; and in the contracting schedule, on days 1, 12 and 13. Cued-recall was assessed after a retention interval (RI) of 2, 6 or 13 days. Consistent with predictions, the expanding schedule generally led to better performance than the other schedules. However, further analyses suggested that the benefit of an expanding schedule may be greater when the RI is longer.