Electrophysiological correlates of semantic processing during encoding of neutral and emotional pictures in patients with ADHD

The current study investigated the relevance of semantic processing and stimulus salience for memory performance in young ADHD patients and healthy control participants. 18 male ADHD patients and 15 healthy control children and adolescents participated in an ERP study during a visual memory paradigm with two different encoding tasks requiring either perceptual or semantic processing of neutral and emotional pictures. ADHD patients and healthy controls both showed a more negative slow-wave in response to task cues signalling semantic as compared to perceptual stimulus processing. In contrast to ADHD patients, healthy control children showed a larger increase in memory performance for deeply processed neutral pictures which was accompanied by a more positive mid-latency ERP component (so-called P300) after stimulus onset. Our results demonstrate that ADHD patients succeeded in allocating neural resources in preparation of different task demands. However, this increase in preparatory activation to the semantic task cue did not suffice to support successful processing and encoding of neutral stimuli to the same extent as in healthy controls. These findings provide evidence that ADHD patients show deficits in translating pre-stimulus mobilization of neural resources to successful memory formation in the absence of salient stimulus material.     

Event-related fMRI of frontotemporal activity during word encoding and recognition in schizophrenia

OBJECTIVE: Neuropsychological studies have demonstrated verbal episodic memory deficits in schizophrenia during word encoding and retrieval. This study examined neural substrates of memory in an analysis that controlled for successful retrieval. METHOD: Event-related blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) was used to measure brain activation during word encoding and recognition in 14 patients with schizophrenia and 15 healthy comparison subjects. An unbiased multiple linear regression procedure was used to model the BOLD response, and task effects were detected by contrasting the signal before and after stimulus onset. RESULTS: Patients attended during encoding and had unimpaired reaction times and normal response biases during recognition, but they had lower recognition discriminability scores, compared with the healthy subjects. Analysis of contrasts was restricted to correct items. Previous findings of a deficit in bilateral prefrontal cortex activation during encoding in patients were reproduced, but patients showed greater parahippocampal activation rather than deficits in temporal lobe activation. During recognition, left dorsolateral prefrontal cortex activation was lower in the patients and right anterior prefrontal cortex activation was preserved, as in the authors' previous study using positron emission tomography. Successful retrieval was associated with greater right dorsolateral prefrontal cortex activation in the comparison subjects, whereas orbitofrontal, superior frontal, mesial temporal, middle temporal, and inferior parietal regions were more active in the patients during successful retrieval. CONCLUSIONS: The pattern of prefrontal cortex underactivation and parahippocampal overactivation in the patients suggests that functional connectivity of dorsolateral prefrontal and temporal-limbic structures is disrupted by schizophrenia. This disruption may be reflected in the memory strategies of patients with schizophrenia, which include reliance on rote rehearsal rather than associative semantic processing.     

Top-down and bottom-up attention to memory: a hypothesis (AtoM) on the role of the posterior parietal cortex in memory retrieval

Recent neuroimaging studies have implicated the posterior parietal cortex in episodic memory retrieval, but there is uncertainty about its specific role. Research in the attentional domain has shown that superior parietal lobe (SPL) regions along the intraparietal sulcus are implicated in the voluntary orienting of attention to relevant aspects of the environment, whereas inferior parietal lobe (IPL) regions at the temporo-parietal junction mediate the automatic allocation of attention to task-relevant information. Here we propose that the SPL and the IPL play conceptually similar roles in episodic memory retrieval. We hypothesize that the SPL allocates top-down attention to memory retrieval, whereas the IPL mediates the automatic, bottom-up attentional capture by retrieved memory contents. By reviewing the existing fMRI literature, we show that the posterior intraparietal sulcus of SPL is consistently active when the need for top-down assistance to memory retrieval is supposedly maximal, e.g., for memories retrieved with low vs. high confidence, for familiar vs. recollected memories, for recognition of high vs. low frequency words. On the other hand, the supramarginal gyrus of IPL is consistently active when the attentional capture by memory contents is supposedly maximal, i.e., for strong vs. weak memories, for vividly recollected vs. familiar memories, for memories retrieved with high vs. low confidence. We introduce a model of episodic memory retrieval that characterizes contributions of posterior parietal cortex.     

Altered neural function during episodic memory encoding and retrieval in major depression

Memory impairments are common in major depression. Neural processing during non‐emotional episodic memory in depressed patients has only sparsely been investigated, since the majority of studies have focused on emotional stimuli. The aim of this study was to explore neural correlates of episodic memory in depressive patients and to assess brain regions related to subsequent memory performance. Forty‐six participants (23 depressed patients) performed a non‐emotional episodic memory encoding and retrieval task while brain activation was measured with functional magnetic resonance imaging. Patients with depression showed decreased activation in the right prefrontal cortex and right cingulate cortex during memory encoding, but increased activation in the right inferior frontal gyrus (IFG) during recognition memory. While a strong association between hippocampal and parahippocampal activation during memory encoding with subsequent memory performance became evident in healthy controls, this relationship was absent in patients with depression. Taken together, these findings demonstrate that memory related brain regions are affected in their appropriate functioning during memory encoding in depressed patients. Therefore, patients with depression may rely to a greater degree on other brain regions such as the IFG during episodic memory retrieval. Hum Brain Mapp 35:4293–4302, 2014. © 2014 Wiley Periodicals, Inc .     

Glucose administration enhances fMRI brain activation and connectivity related to episodic memory encoding for neutral and emotional stimuli

Glucose enhances memory in a variety of species. In humans, glucose administration enhances episodic memory encoding, although little is known regarding the neural mechanisms underlying these effects. Here we examined whether elevating blood glucose would enhance functional MRI (fMRI) activation and connectivity in brain regions associated with episodic memory encoding and whether these effects would differ depending on the emotional valence of the material. We used a double-blind, within-participants, crossover design in which either glucose (50 g) or a saccharin placebo were administered before scanning, on days approximately 1 week apart. We scanned healthy young male participants with fMRI as they viewed emotionally arousing negative pictures and emotionally neutral pictures, intermixed with baseline fixation. Free recall was tested at 5 min after scanning and again after 1 day. Glucose administration increased activation in brain regions associated with successful episodic memory encoding. Glucose also enhanced activation in regions whose activity was correlated with subsequent successful recall, including the hippocampus, prefrontal cortex, and other regions, and these effects differed for negative vs. neutral stimuli. Finally, glucose substantially increased functional connectivity between the hippocampus and amygdala and a network of regions previously implicated in successful episodic memory encoding. These findings fit with evidence from nonhuman animals indicating glucose modulates memory by selectively enhancing neural activity in brain regions engaged during memory tasks. Our results highlight the modulatory effects of glucose and the importance of examining both regional changes in activity and functional connectivity to fully characterize the effects of glucose on brain function and memory.     

Emotional memory in ADHD patients with and without comorbid ODD/CD

The present study investigated whether children and adolescents with attention deficit hyperactivity disorder (ADHD) and comorbid oppositional defiant disorder (ODD) or conduct disorder (CD) show a memory bias for negative emotional pictures. Subjects participated in an incidental memory paradigm involving neutral, positive and negative pictures. In ADHD only patients, memory performance was enhanced to the level of healthy control subjects both by positive and negative pictures, whereas in ADHD patients with comorbid ODD/CD, memory performance was only normalized by negative pictures.     

Left superior parietal cortex involvement in writing: integrating fMRI with lesion evidence

Writing is a uniquely human skill that we utilize nearly everyday. Lesion studies in patients with Gerstmann's syndrome have pointed to the parietal cortex as being critical for writing. Very little information is, however, available about the precise anatomical location of brain regions subserving writing in normal healthy individuals. In this study, we used functional magnetic resonance imaging (fMRI) to investigate parietal lobe function during writing to dictation. Significant clusters of activation were observed in left superior parietal lobe (SPL) and the dorsal aspects of the inferior parietal cortex (IPC) bordering the SPL. Localized clusters of activation were also observed in the left premotor cortex, sensorimotor cortex and supplementary motor area. No activation cluster was observed in the right hemisphere. These results clearly indicate that writing appears to be primarily organized in the language-dominant hemisphere. Further analysis revealed that within the parietal cortex, activation was significantly greater in the left SPL, compared to left IPC. Together with lesion studies, findings from the present study provide further evidence for the essential role of the left SPL in writing. Deficits to the precise left hemisphere parietal cortex regions identified in the present study may specifically underlie disorders of writing observed in Gerstmann's syndrome and apractic agraphia.     

Differences of cerebral activation between superior and inferior learners during motor sequence encoding and retrieval

Cerebral activation during memory encoding and retrieval might depend on subjects' learning capacity, either by corresponding to better performance in superior learners or by reflecting increased effort in inferior learners. To investigate these alternative hypotheses, the study compared cerebral activation during encoding and retrieval of a motor sequence in groups of subjects with superior and inferior learning performances. Ten healthy subjects underwent functional magnetic resonance imaging (fMRI) while performing a motor sequence encoding paradigm (i.e. finger tapping sequence) and a retrieval paradigm (i.e. reproduction of the learned sequence). Subjects were divided into superior and inferior learners according to the correctness of sequence reproduction during retrieval. During encoding, there was strong bilateral activation in the middle frontal gyrus, the supplementary motor area (SMA), the lateral parietal lobe and the cerebellum. During retrieval, again strong activation was found in identical areas of the prefrontal cortex, the parietal lobe and the cerebellum. During encoding, inferior learners showed more left-sided activations in the left middle frontal and inferior parietal gyri. Superior learners showed increased activation in the corresponding right-sided brain areas during encoding as well as during retrieval. Differences of cerebral activations in the prefrontal and parietal cortex during encoding and retrieval were found to be related to retrieval performance, i.e. success and effort. Further intervention studies are needed to assess whether these interindividual differences are the cause or the consequence of differences in memory performance.     

Shifting-related brain magnetic activity in attention-deficit/hyperactivity disorder.

BACKGROUND: Current theories suggest a role for frontal-striatal circuits in the pathogenesis of attention-deficit/hyperactivity disorder (ADHD). METHODS: We used magnetoencephalography (MEG) to measure event-related brain activity during a simplified version of the Wisconsin Card Sorting Test in children with DSM-IV combined type ADHD (ADHD-C) or predominantly inattentive type ADHD (ADHD-PI) and in age- and intelligence-matched control children. RESULTS: In control children, set-shifting cues evoked a higher degree of activation in the medial temporal lobe (MTL) between 200 and 300 msec than non-shifting cues, with MTL activation predicting later activity in left anterior cingulate cortex (ACC) (at 400-500 msec). This MTL-ACC response pattern was diminished in children with ADHD. By contrast, children with ADHD showed early activity in regions barely activated in control children, such as left inferior parietal lobe and posterior superior temporal gyrus. CONCLUSIONS: These preliminary data support theories of frontal dysfunction in ADHD but also suggest that deficits in higher-level functions might be secondary to disruptions in earlier limbic processes.     

Anomalous prefrontal-subcortical activation in familial pediatric bipolar disorder: a functional magnetic resonance imaging investigation

BACKGROUND: The neurobiological features of pediatric bipolar disorder (BD) are largely unknown. Children and adolescents with BD may be important to study with functional neuroimaging techniques because of their unique status of early-onset BD and high familial loading for the disorder. Neuroimaging studies of adults with BD have implicated the dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC) in the development of this disorder. OBJECTIVES: To study children and adolescents with BD via functional magnetic resonance imaging using cognitive and affective tasks and to examine possible abnormalities in the DLPFC and ACC, as well as selected subcortical areas, in pediatric familial BD. DESIGN: We evaluated 12 male subjects aged 9 to 18 years with BD who had at least 1 parent with BD as well as 10 age- and IQ-matched healthy male controls. Stimulants were discontinued for at least 24 hours; other medications were continued. Subjects underwent functional magnetic resonance imaging at 3 T while performing a 2-back visuospatial working memory task and an affective task involving the visualization of positively, neutrally, or negatively valenced pictures. SETTING: An academic referral setting, drawing from the Bay Area of San Francisco, Calif. RESULTS: Compared with controls, for the visuospatial working memory task, subjects with BD had greater activation in several areas including the bilateral ACC, left putamen, left thalamus, left DLPFC, and right inferior frontal gyrus. Controls had greater activation in the cerebellar vermis. In viewing negatively valenced pictures, subjects with BD had greater activation in the bilateral DLPFC, inferior frontal gyrus, and right insula. Controls had greater activation in the right posterior cingulate gyrus. For positively valenced pictures, subjects with BD had greater activation in the bilateral caudate and thalamus, left middle/superior frontal gyrus, and left ACC, whereas controls had no areas of greater activation. CONCLUSIONS: Children and adolescents with BD may have underlying abnormalities in the regulation of prefrontal-subcortical circuits. Further functional magnetic resonance imaging studies of attention and mood with greater sample sizes are needed.     

Testosterone levels in healthy men are related to amygdala reactivity and memory performance

Testosterone is a steroid hormone thought to influence both emotional and cognitive functions. It is unknown, however, if testosterone also affects the interaction between these two domains, such as the emotional arousal-induced enhancement of memory. Healthy subjects (N=234) encoded pictures taken from the International Affective Picture System (IAPS) during functional magnetic resonance imaging (fMRI) and underwent a free recall test 10 min after memory encoding. We show that higher endogenous testosterone levels at encoding were associated with higher arousal ratings of neutral pictures in men. fMRI analysis revealed that higher testosterone levels were related to increased brain activation in the amygdala during encoding of neutral pictures. Moreover, endogenous testosterone levels were positively correlated with the number of freely recalled neutral pictures. No such relations were found in women. These findings point to a male-specific role for testosterone in enhancing memory by increasing the biological salience of incoming information.     

Crossmodal emotional integration in major depression

Major depression goes along with affective and social-cognitive deficits. Most research on affective deficits in depression has, however, only focused on unimodal emotion processing, whereas in daily life, emotional perception is often highly dependent on the evaluation of multimodal inputs. We thus investigated emotional audiovisual integration in patients with depression and healthy subjects. Subjects rated the expression of happy, neutral and fearful faces while concurrently being exposed to emotional or neutral sounds. Results demonstrated group differences in left inferior frontal gyrus and inferior parietal cortex when comparing incongruent to congruent happy facial conditions, mainly due to a failure of patients to deactivate these regions in response to congruent stimulus pairs. Moreover, healthy subjects decreased activation in right posterior superior temporal gyrus/sulcus and midcingulate cortex when an emotional stimulus was paired with a neutral rather than another emotional one. In contrast, patients did not show such deactivation when neutral stimuli were integrated. These results demonstrate aberrant neural response in audiovisual processing in depression, indicated by failure to deactivate regions involved in inhibition and salience processing when congruent and neutral audiovisual stimuli pairs are integrated, providing a possible mechanism of constant arousal and readiness to act in this patient group.     

Neural correlates of emotional recognition memory in schizophrenia: effects of valence and arousal

Schizophrenia patients are often impaired in their memory for emotional events compared with healthy subjects. Investigations of the neural correlates of emotional memory in schizophrenia patients are scarce in the literature. The present study aimed to compare cerebral activations in schizophrenia patients and healthy controls during memory retrieval of emotional images that varied in both valence and arousal. In a study with functional magnetic resonance imaging, 37 schizophrenia patients were compared with 37 healthy participants while performing a yes/no recognition paradigm with positive, negative (differing in arousal intensity) and neutral images. Schizophrenia patients performed worse than healthy controls in all experimental conditions. They showed less cerebral activation in limbic and prefrontal regions than controls during retrieval of negatively valenced stimuli, but had a similar pattern of brain activation compared with controls during retrieval of positively valenced stimuli (particularly in the high arousal condition) in the cerebellum, temporal lobe and prefrontal cortex. Both groups demonstrated increased brain activations in the high relative to low arousing conditions. Our results suggest atypical brain function during retrieval of negative pictures, but intact functional circuitry of positive affect during episodic memory retrieval in schizophrenia patients. The arousal data revealed that schizophrenia patients closely resemble the control group at both the behavioral and neurofunctional level.     

Associations evoked during memory encoding recruit the context-network

An extensive cortical network consisting of structures in the medial temporal lobe (hippocampus and parahippocampal cortex), lateral parietal cortex, retrosplenial cortex, and medial prefrontal cortex has recently attracted attention in cognitive neuroscience research, linking the network to both episodic memory and spatial processing. It has been suggested that its function may be best characterized as supporting the processing of contextual associations (context network). In this study, we explored whether the role of this network in contextual processing extends to associations that are evoked in a spontaneous manner. In a novel memory encoding task, participants indicated whether they encoded pictures (objects and novel faces) based on an evoked association or based on a perceptual feature. Memory encoding with subjective associations enhanced memory formation relative to feature-based encoding, and this effect was more pronounced for rapidly evoked associations. Functional magnetic resonance imaging during encoding yielded significant activations in all regions of the context network, i.e., medial prefrontal cortex, lateral parietal cortex, retrosplenial cortex, and posterior medial temporal lobe for the associative vs. feature-based comparisons. The low number of misses did not permit the analysis of a subsequent memory contrast. Our data suggest that the context network, which includes the posterior hippocampus and parahippocampal cortex, might support the linkage of external stimuli to long-term memory representations.     

Anterior insula hyperactivation in ADHD when faced with distracting negative stimuli

Patients with attention deficit hyperactivity disorder (ADHD) suffer from poor emotion regulation that might arise from problems in the distribution of attentional resources when confronted with emotional distractors. Previous studies investigating the neurocognitive basis of these problems remain inconclusive. Moreover, most of these studies did not exclude participants with comorbidity, particularly of conduct or oppositional defiant disorder. The aim of this study was to assess alterations in fronto‐limbic activation in ADHD adolescents specifically during negative distractors in an emotional attention task. For this purpose, we used functional magnetic resonance imaging to assess 25 boys with noncomorbid ADHD and 25 typically developing (TD) boys while they performed an emotional attention task with positive, negative, and neutral emotional distractors. Boys with ADHD had increased activation relative to TD boys specifically during the negative valenced stimuli in an emotional processing network comprising left anterior insula reaching into the inferior frontal gyrus. The findings suggest altered salience processing in ADHD of negative valenced emotional stimuli that may lead to higher distractibility in ADHD specifically when faced with negative emotional distractors.     

Medial prefrontal cortex activity during memory encoding of pictures and its relation to symptomatic improvement after citalopram treatment in patients with major depression

Background

Brain imaging studies of major depressive disorder have shown alterations in the brain regions typically involved in episodic memory, including the prefrontal cortex and medial temporal areas. Some studies of major depressive disorder have linked episodic memory performance to treatment response. In this study, we sought to identify brain regions whose activity, measured during the encoding of pictures, predicted symptomatic improvement after 8 weeks of citalopram treatment.

Methods

We included 20 unmedicated depressed patients. These patients performed an episodic recognition memory task during functional magnetic resonance imaging. During the encoding phase, 150 pictures depicting emotionally positive, negative or neutral content were presented, and the participants were required to classify each picture according to its emotional valence. The same 150 pictures were presented, along with 150 new ones, for a recognition task. We asked participants to distinguish the old pictures from the new ones. We assessed symptom severity by use of the 21-item Hamilton Rating Scale for Depression (HAM-D) at baseline and after 8 weeks of citalopram treatment. We performed subsequent memory effect analyses using SPM2 software. We explored the relation between brain activation during successful encoding of pictures and symptomatic improvement.

Results

Patients showed a mean symptomatic improvement of 54.5% on the HAM-D after 8 weeks. Symptomatic improvement was significantly and positively correlated with picture recognition memory accuracy. We also found that the activity of the ventromedial prefrontal cortex and anterior cingulate cortex during successful encoding was significantly correlated with symptomatic improvement. Finally, we found greater activation in the ventromedial prefrontal cortex during the successful encoding of positive pictures in comparison with neutral pictures.

Limitations

During the recognition memory task, 5 participants (among the best responders to treatment) were not included in the valence-specific analyses because they had very few errors. A more challenging task would have allowed the inclusion of most patients.

Conclusion

Different types of functional imaging paradigms have been used to explore whether the activity of specific brain regions measured at baseline is predictive of a better response to treatment in major depressive disorder. Among these regions, the medial prefrontal cortex and anterior cingulate cortex usually show the strongest predictive value. According to our results, the medial prefrontal cortex and anterior cingulate cortex could have an effect on treatment response in major depressive disorder by contributing to the successful encoding of positively valenced information.     

The influence of emotional distraction on verbal working memory: an fMRI investigation comparing individuals with schizophrenia and healthy adults

The ability to maintain information over short periods of time (i.e., working memory) is critically important in a variety of cognitive functions including language, planning, and decision-making. Recent functional Magnetic Resonance Imaging (fMRI) research with healthy adults has shown that brain activations evoked during the delay interval of working memory tasks can be reduced by the presentation of distracting emotional events, suggesting that emotional events may take working-memory processes momentarily offline. Both executive function and emotional processing are disrupted in schizophrenia, and here we sought to elucidate the effect of emotional distraction upon brain activity in schizophrenic and healthy adults performing a verbal working memory task. During the delay period between the memoranda and memory probe items, emotional and neutral distractors differentially influenced brain activity in these groups. In healthy adults, the hemodynamic response from posterior cingulate, orbital frontal cortex, and the parietal lobe strongly differentiated emotional from neutral distractors. In striking contrast, schizophrenic adults showed no significant differences in brain activation when processing emotional and neutral distractors. Moreover, the influence of emotional distractors extended into the memory probe period in healthy, but not schizophrenic, adults. The results suggest that although emotional items are highly salient for healthy adults, emotional items are no more distracting than neutral ones to individuals with schizophrenia.     

Task-specific hypoactivation in prefrontal and temporoparietal brain regions during motor inhibition and task switching in medication-naive children and adolescents with attention deficit hyperactivity disorder

OBJECTIVE: A relatively small number of functional imaging studies of attention deficit hyperactivity disorder (ADHD) have shown abnormal prefrontal and striatal brain activation during tasks of motor response inhibition. However, the potential confound of previous medication exposure has not yet been addressed, and no functional imaging study exists to date on medication-naive children and adolescents with ADHD. The aim of this study was to investigate the neural substrates of a range of motor and cognitive inhibitory functions in a relatively large group of children and adolescents with ADHD who had never previously been exposed to medication. METHOD: Nineteen boys with ADHD and 27 healthy age- and IQ-matched boys underwent functional MRI to compare brain activation during performance of tasks that assessed motor response inhibition (go/no go task), cognitive interference inhibition (motor Stroop task), and cognitive flexibility (switch task). RESULTS: Boys with ADHD showed decreased activation in the left rostral mesial frontal cortex during the go/no go task and decreased activation in the bilateral prefrontal and temporal lobes and right parietal lobe during the switch task. No significant group differences were observed during motor Stroop task performance. CONCLUSION: Abnormal brain activation was observed in medication-naive children and adolescents with ADHD during tasks involving motor inhibition and task switching, suggesting that hypoactivation in this patient group is unrelated to long-term stimulant exposure. Furthermore, functional abnormalities are task-specific and extend from frontostriatal to parietal and temporal cortices.     

fMRI studies of successful emotional memory encoding: A quantitative meta-analysis

Over the past decade, fMRI techniques have been increasingly used to interrogate the neural correlates of successful emotional memory encoding. These investigations have typically aimed to either characterize the contributions of the amygdala and medial temporal lobe (MTL) memory system, replicating results in animals, or delineate the neural correlates of specific behavioral phenomena. It has remained difficult, however, to synthesize these findings into a systems neuroscience account of how networks across the whole-brain support the enhancing effects of emotion on memory encoding. To this end, the present study employed a meta-analytic approach using activation likelihood estimates to assess the anatomical specificity and reliability of event-related fMRI activations related to successful memory encoding for emotional versus neutral information. The meta-analysis revealed consistent clusters within bilateral amygdala, anterior hippocampus, anterior and posterior parahippocampal gyrus, the ventral visual stream, left lateral prefrontal cortex and right ventral parietal cortex. The results within the amygdala and MTL support a wealth of findings from the animal literature linking these regions to arousal-mediated memory effects. The consistency of findings in cortical targets, including the visual, prefrontal, and parietal cortices, underscores the importance of generating hypotheses regarding their participation in emotional memory formation. In particular, we propose that the amygdala interacts with these structures to promote enhancements in perceptual processing, semantic elaboration, and attention, which serve to benefit subsequent memory for emotional material. These findings may motivate future research on emotional modulation of widespread neural systems and the implications of this modulation for cognition.     

Effects of an ambient odor on brain activations during episodic retrieval of objects

This study investigated the brain areas involved in episodic memory retrieval of pictures depending on the characteristics of the contextual environment during encoding (i.e. presence or absence of an odor). In the first stage, subjects were presented with a series of 32 pictures. Half of the pictures were presented while the subjects smelled an odor (vanillin). No particular odor was associated with the presentation of the other half of the pictures. Two weeks later, a retrieval task was performed in which the same pictures were presented during an fMRI session but without any odor association involved. The results show that both conditions activate a common episodic memory network including the hippocampal formation. Compared with the “encoding without odor” condition, the “encoding with odor” condition shows greater activations in temporal, parietal and frontal cortices, notably within the area of the orbitofrontal cortex which constitutes a main site of the secondary olfactory cortex. No activated areas were observed in the inverse contrast. These results highlight the complexity of the networks involved in episodic memory according to the context during encoding.