Ventral Frontal Lobe Research Articles

The neurophysiology of closed-loop auditory stimulation in sleep: A magnetoencephalography study.

Closed-loop auditory stimulation (CLAS) is a brain modulation technique in which sounds are timed to enhance or disrupt endogenous neurophysiological events. CLAS of slow oscillation up-states in sleep is becoming a popular tool to study and enhance sleep's functions, as it increases slow oscillations, evokes sleep spindles and enhances memory consolidation of certain tasks. However, few studies have examined the specific neurophysiological mechanisms involved in CLAS, in part because of practical limitations to available tools. To evaluate evidence for possible models of how sound stimulation during brain up-states alters brain activity, we simultaneously recorded electro- and magnetoencephalography in human participants who received auditory stimulation across sleep stages. We conducted a series of analyses that test different models of pathways through which CLAS of slow oscillations may affect widespread neural activity that have been suggested in literature, using spatial information, timing and phase relationships in the source-localized magnetoencephalography data. The results suggest that auditory information reaches ventral frontal lobe areas via non-lemniscal pathways. From there, a slow oscillation is created and propagated. We demonstrate that while the state of excitability of tissue in auditory cortex and frontal ventral regions shows some synchrony with the electroencephalography (EEG)-recorded up-states that are commonly used for CLAS, it is the state of ventral frontal regions that is most critical for slow oscillation generation. Our findings advance models of how CLAS leads to enhancement of slow oscillations, sleep spindles and associated cognitive benefits and offer insight into how the effectiveness of brain stimulation techniques can be improved.

Multisensory interactions of face and vocal information during perception and memory in ventrolateral prefrontal cortex.

The ventral frontal lobe is a critical node in the circuit that underlies communication, a multisensory process where sensory features of faces and vocalizations come together. The neural basis of face and vocal integration is a topic of great importance since the integration of multiple sensory signals is essential for the decisions that govern our social interactions. Investigations have shown that the macaque ventrolateral prefrontal cortex (VLPFC), a proposed homologue of the human inferior frontal gyrus, is involved in the processing, integration and remembering of audiovisual signals. Single neurons in VLPFC encode and integrate species-specific faces and corresponding vocalizations. During working memory, VLPFC neurons maintain face and vocal information online and exhibit selective activity for face and vocal stimuli. Population analyses indicate that identity, a critical feature of social stimuli, is encoded by VLPFC neurons and dictates the structure of dynamic population activity in the VLPFC during the perception of vocalizations and their corresponding facial expressions. These studies suggest that VLPFC may play a primary role in integrating face and vocal stimuli with contextual information, in order to support decision making during social communication. This article is part of the theme issue 'Decision and control processes in multisensory perception'.

Forebrain Response to Breathing in Humans during Awake and Unconscious States

Although the brainstem has long been studied as the site responsible for automatic breathing, little is known about how the forebrain responds to breathing in humans during awake and unconscious states. Here, we tested the hypotheses (1) that forebrain sites will exhibit responses to phases of breathing and (2) these responses will differ based on type of breathing (nasal, oral, or via an endotracheal tube), level of consciousness, and whether the subject is breathing automatically or being mechanically ventilated. We studied five neurosurgical patients undergoing intracranial electroencephalography (IEEG). We recorded respiration using a oral/nasal thermistor, nasal pressure transducer, and chest/abdominal plethysmography belts. Under general anesthesia, additional respiratory measures were obtained using a standard clinical ventilator. Using spectral and bispectrum IEEG analysis, we found that oscillations entrained to the breath phase (inspiration/exhalation) during both nasal and mouth only breathing in numerous cortical and subcortical sites while awake. Interestingly, this entrainment appeared to increase under general anesthesia when the subjects were unconscious and breathing automatically, an effect which was altered when the subjects were mechanically ventilated. The sites that had the most significant entrainment localized to the sensorimotor cortex, ventral frontal lobe, and limbic system. These findings suggest that forebrain oscillations respond to all types of breathing and forebrain entrainment to the respiratory cycle may increase during unconsciousness. This interesting finding may prove critical for a predictive coding model for breathing, which might serve as a defense mechanism to ensure adequate ventilation.

Viewing orbitofrontal cortex contributions to decision-making through the lens of object recognition.

Decision neuroscience research has consistently implicated orbitofrontal and adjacent ventromedial prefrontal cortex in value-based decision-making. These areas are thought to reflect subjective value, a generic indicator of the personal motivational relevance of different options that allows them to be compared on a common scale. There are a number of unanswered questions arising from this model. We review findings from studies in patients with focal damage to the ventral frontal lobe that led us to reconsider how decision options are evaluated, applying perspectives from research on object recognition in the ventral visual stream. While decision-making is often approached from an abstract economic perspective in the lab, most of our everyday decisions, whether about food, goods, or people, are between directly perceived complex objects made up of multiple value-predictive attributes. It is not clear how multiple attributes are integrated to produce a global value estimate. We know the objects themselves are represented in the ventral visual stream at different levels of complexity, ranging from individual features to unique combinations of such features, but what about the values of those objects? Here, we suggest distinctions between configural and elemental evaluation echoing distinctions in visual processing. We discuss evidence that orbitofrontal-ventromedial prefrontal cortex is not required for all value-based decisions, but rather is specifically critical for recognizing value when it is predicted by configural relationships between attributes. We also consider how this perspective connects with emerging views of orbitofrontal cortex as an abstract cognitive map, and the debate on whether subjective value is a neurobiologically meaningful construct. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Mixed selectivity for visual features and economic value in the primate orbitofrontal cortex

Primates use their acute sense of vision not only to identify objects, but also to assess their value, that is, their potential for benefit or harm. How the brain transforms visual information into value information is still poorly understood, but recent findings suggest a key role for the orbitofrontal cortex (OFC). The OFC includes several cytoarchitectonic areas within the ventral frontal lobe, and has a long-recognized role in representing object value and organizing value-driven behavior. One of the OFC’s most striking anatomical features is the massive, direct input it receives from the inferotemporal cortex, a ventral temporal region implicated in object identification. A natural hypothesis, therefore, is that in addition to well-documented value coding properties, OFC neurons may also represent visual features in a manner similar to neurons in the ventral visual stream. To test this hypothesis, we recorded OFC neurons in macaque monkeys performing behavioral tasks in which the value of visible objects was manipulated independently from their visual features. Preliminary findings include a subset of OFC cells that were modulated by object value, but only in response to objects that shared a particular visual feature (e.g. the color red). This form of ‘mixed’ selectivity suggests that the OFC may be an intermediate computational stage between visual identification and value retrieval. Moreover, recent work showing similar mixed value-feature selectivity in inferotemporal cortex neurons suggests that neural mechanisms of object valuation may be distributed over a continuum of cortical regions, rather than compartmentalized in a strict hierarchy.

Network connectivity determines cortical thinning in early Parkinson\u2019s disease progression

Here we test the hypothesis that the neurodegenerative process in Parkinson’s disease (PD) moves stereotypically along neural networks, possibly reflecting the spread of toxic alpha-synuclein molecules. PD patients (n = 105) and matched controls (n = 57) underwent T1-MRI at entry and 1 year later as part of the Parkinson’s Progression Markers Initiative. Over this period, PD patients demonstrate significantly greater cortical thinning than controls in parts of the left occipital and bilateral frontal lobes and right somatomotor-sensory cortex. Cortical thinning is correlated to connectivity (measured functionally or structurally) to a “disease reservoir” evaluated by MRI at baseline. The atrophy pattern in the ventral frontal lobes resembles one described in certain cases of Alzheimer’s disease. Our findings suggest that disease propagation to the cortex in PD follows neuronal connectivity and that disease spread to the cortex may herald the onset of cognitive impairment.

Altered basal ganglia-cortical functional connections in frontal lobe epilepsy: A resting-state fMRI study

ObjectivesThe purpose of this study was to investigate alterations of basal ganglia-cortical functional connections in patients with frontal lobe epilepsy (FLE). MethodResting-state functional magnetic resonance imaging (fMRI) data were gathered from 19 FLE patients and 19 age- and gender-matched healthy controls. Functional connectivity (FC) analysis was used to assess the functional connections between basal ganglia and cerebral cortex. Regions of interest, including the left/right caudate, putamen, pallidum and thalamus, were selected as the seeds. Two sample t-test was used to determine the difference between patients and controls, while controlling the age, gender and head motions. ResultsCompared with controls, FLE patients demonstrated increased FCs between basal ganglia and regions including the right fusiform gyrus, the bilateral cingulate gyrus, the precuneus and anterior cingulate gyrus. Reduced FCs were mainly located in a range of brain regions including the bilateral middle occipital gyrus, the ventral frontal lobe, the right putamen, the left fusiform gyrus and right rolandic operculum. In addition, the relationships between basal ganglia-cingulate connections and durations of epilepsy were also found. ConclusionThe alterations of functional integrity within the basal ganglia, as well as its connections to limbic and ventral frontal areas, indicate the important roles of the basal ganglia-cortical functional connections in FLE, and provide new insights in the pathophysiological mechanism of FLE.

Inactivation of Primate Prefrontal Cortex Impairs Auditory and Audiovisual Working Memory.

The ventral frontal lobe, or inferior frontal gyrus, plays an important role in audiovisual communication in the human brain. Studies with nonhuman primates have found that neurons within ventral prefrontal cortex (VLPFC) encode both faces and vocalizations and that VLPFC is active when animals need to remember these social stimuli. In the present study, we temporarily inactivated VLPFC by cooling the cortex while nonhuman primates performed a working memory task. This impaired the ability of subjects to remember a face and vocalization pair or just the vocalization alone. Our work highlights the importance of the primate VLPFC in the processing of faces and vocalizations in a manner that is similar to the inferior frontal gyrus in the human brain.

Corpus callosal abnormalities in dogs.

BackgroundCorpus callosal abnormalities (CCA) in dogs have been only sporadically reported and are poorly characterized.Hypothesis/ObjectivesTo describe the clinical presentation and magnetic resonance imaging (MRI) characteristics of dogs with CCA.AnimalsFifteen client‐owned dogs.MethodsRetrospective study. Records of the contributing institutions were reviewed to identify dogs diagnosed with malformations affecting the corpus callosum (CC); cases in which the CCA was thought to be secondary were excluded.ResultsThe most represented breeds were Staffordshire Bull Terriers (5/15) and Miniature Schnauzers (3/15; n = 3, 20%) and the mean age at time of presentation of 19 months (range 3–81 months). The clinical signs most commonly reported were adipsia/hypodipsia with associated hypernatremia (12/15), tremors (6/15), and seizures (6/15). Review of the MR images revealed that 10 dogs had absence of the rostral CC and hypoplasia of the caudal portion, 4 dogs had a diffusely hypoplastic and dysplastic CC, and 1 dog had a diffusely hypoplastic CC. In 14 cases, there was abnormal cortical development with fusion of the ventral frontal lobes and part of the diencephalon, indicating lobar holoprosencephaly.Conclusions and Clinical ImportancePrevious literature has mainly associated CCA with adipsia and only 12 of 15 dogs in the current series demonstrated this abnormality. There are different degrees of the malformation but in 10 dogs the rostral portion of the CC is most severely affected. Fourteen dogs have simultaneous fusion of the midline structures rostral to the CC; this region has several structures involved in thirst regulation and might explain this derangement.

Social Signals in Primate Orbitofrontal Cortex

Primate evolution produced an increased capacity to respond flexibly to varying social contexts as well as expansion of the prefrontal cortex. Despite this association, how prefrontal neurons respond to social information remains virtually unknown. People with damage to their orbitofrontal cortex (OFC) struggle to recognize facial expressions, make poor social judgments, and frequently make social faux pas. Here we test explicitly whether neurons in primate OFC signal social information and, if so, how such signals compare with responses to primary fluid rewards. We find that OFC neurons distinguish images that belong to socially defined categories, such as female perinea and faces, as well as the social dominance of those faces. These modulations signaled both how much monkeys valued these pictures and their interest in continuing to view them. Far more neurons signaled social category than signaled fluid value, despite the stronger impact of fluid reward on monkeys' choices. These findings indicate that OFC represents both the motivational value and attentional priority of other individuals, thus contributing to both the acquisition of information about others and subsequent social decisions. Our results betray a fundamental disconnect between preferences expressed through overt choice, which were primarily driven by the desire for more fluid, and preferential neuronal processing, which favored social computations.

Changes in appetite, food preference, and eating habits in frontotemporal dementia and Alzheimer’s disease

Background: Despite numerous reports of changes in satiety, food preference, and eating habits in patients with frontotemporal dementia, there have been few systematic studies. Objectives: To investigate the frequency of...

Brain metabolic changes associated with symptom factor improvement in major depressive disorder

Background: Symptoms of major depressive disorder (MDD) have been linked to regional brain function through imaging studies of symptom provocation in normal control subjects and baseline studies of subjects with MDD. We examined associations between change in depressive symptom factors and change in regional brain metabolism from before to after treatment of MDD. Methods: Thirty-nine outpatients with MDD underwent 18F-fluorodeoxyglucose positron emission tomography scanning before and after treatment with either paroxetine or interpersonal psychotherapy. Associations were determined between changes in regional brain metabolism and changes in four Hamilton Depression Rating Scale factors (anxiety/somatization [ANX], psychomotor retardation [PR], cognitive disturbance [COGN], and sleep disturbance) and two corresponding Profile of Mood States subscales (tension [TENS] and fatigue [FATIG]). Results: Improvement in ANX, PR, TENS, and FATIG factors was associated with decreasing ventral frontal lobe metabolism. Improvement in ANX and TENS was also associated with decreasing ventral anterior cingulate gyrus (AC) and anterior insula activity, whereas improvement in PR was associated with increasing dorsal AC activity. COGN improvement was associated with increasing dorsolateral prefrontal cortex metabolism. Conclusions: Brain regions that show significant relationships with symptom provocation in normal control subjects have similar relationships with MDD symptoms as they improve with treatment.

Single-shot EPI with signal recovery from the susceptibility-induced losses.

A major problem in the gradient-recalled echo-planar imaging (EPI) method that also uses a long echo time (TE) is the severe signal loss in regions with large static field inhomogeneities. These regions include the ventral frontal, medial temporal, and inferior temporal lobes, which experience inhomogeneities induced by susceptibility effects commonly found near air/tissue interfaces. For functional magnetic resonance imaging (fMRI) studies that use both gradient-recalled EPI at relatively long TE and high-field scanners, this signal loss is severe, preventing investigation of certain human cognitive processes that involve these regions, such as memory and attention. Methods have been developed to recover this signal loss; however, most of them require multiple excitations and thus compromise temporal resolution. In this report, a new technique is described which achieves good signal recovery within a single excitation. It is anticipated that this technique will prove useful for fMRI studies in inhomogeneous areas that require high temporal resolution.

Profound Amnesia and Confabulation Following Traumatic Brain Injury

Amnesia and confabulation may persist following acute aneurysmal hemorrhage of the anterior communicating artery, chronic alcoholic Korsakoff’s syndrome, and late-stage dementia of the Alzheimer type. However, there is a paucity of information regarding the persistence of these symptoms following traumatic brain injury. We present the case of JL, a 43-year-old male with persistent and severe anterograde amnesia for verbal and visual information with co-occurring provoked confabulation which persists well into the chronic phase of recovery after a severe traumatic brain injury. Neuropsychological testing at 7 weeks post-injury demonstrated severe anterograde amnesia with co-occurring confabulation. Follow-up testing at 9.5 months post-injury showed persistent and severe anterograde amnesia and provoked confabulation despite superior non-verbal intelligence and above average attentional and perceptual abilities. Late computed tomography showed chronic hypodense regions in the temporal lobes, bilaterally (L > R), and in the region of the left ventrolateral frontal lobe. This case demonstrates that anterograde amnesia and provoked confabulation may persist long after the acute phase of recovery after traumatic brain injury, and also supports previous research which asserts that medial temporal lobe damage must be accompanied by ventral frontal lobe pathology to produce the amnestic-confabulatory syndrome.

Which neuropsychiatric and behavioural features distinguish frontal and temporal variants of frontotemporal dementia from Alzheimer's disease?

OBJECTIVESTo investigate the prevalence of changes in mood, personality, and behaviour in frontotemporal dementia (FTD) and Alzheimer's disease (AD) and hence, which features reliably distinguish between them. To establish whether...

Face and voice expression identification in patients with emotional and behavioural changes following ventral frontal lobe damage

Impairments in the identification of facial and vocal emotional expression were demonstrated in a group of patients with ventral frontal lobe damage who had socially inappropriate behaviour. The expression identification impairments could occur independently of perceptual impairments in facial recognition, voice discrimination, or environmental sound recognition. The face and voice expression problems did not necessarily occur together in the same patients, providing an indication of separate processing. Poor performance on both expression tests was correlated with the degree of alteration of emotional experience reported by the patients. There was also a strong positive correlation between the degree of altered emotional experience and the severity of the behavioural problems (e.g. disinhibition) found in these patients. A comparison group of patients with brain damage outside the ventral frontal lobe region, without these behavioural problems, was unimpaired on the face expression identification test, was significantly less impaired at vocal expression identification and reported little subjective emotional change. The expression identification deficits in ventral frontal patients may contribute to the abnormal behaviour seen after frontal lesions, and have implications for rehabilitation.

Neuropsychological and neuroanatomical correlates of confabulation

In the present exploratory investigation we report nine confabulatory patients of comparable age, education, and general level of intelligence in the acute epoch of recovery after rupture and clipping of ACoA aneurysms. Five of the nine cases had "spontaneous" confabulation, severe anterograde amnesia, markedly poor attentional and executive functions, and denial of illness. These patients all had multiple lesions that involved basal forebrain, ventral frontal lobe, and striatum. The other four patients manifested only "momentary" or "provoked" confabulations. These patients also had severe anterograde amnesia but showed relatively mild deficits in executive functions. These patients had lesions restricted to the basal forebrain except for one who had additional orbital frontal damage. Analysis of these two groups of confabulatory patients suggests that there is a common profile of deficits and anatomic foundation associated with confabulation; "spontaneous" confabulation appears to require extensive, simultaneous disruption of medial basal forebrain and frontal cognitive systems resulting in profound executive and memory deficits, whereas more limited lesions to the basal forebrain or orbital frontal cortex will result in "transient" or "provoked" confabulatory responses and a more restricted profile of cognitive deficits.

Brain mechanisms for invariant visual recognition and learning

Mechanisms by which the brain could perform invariant recognition of objects including faces are addressed neurophysiologically, and then a computational model of how this could occur is described. Some neurons that respond primarily to faces are found in the macaque cortex in the anterior part of the superior temporal sulcus (in which region neurons are especially likely to be tuned to facial expression, and to face movement involved in gesture). They are also found more ventrally in the TE areas which form the inferior temporal gyrus. Here the neurons are more likely to have responses related to the identity of faces. These areas project on to the amygdala and orbitofrontal cortex, in which face-selective neurons are also found. Quantitative studies of the responses of the neurons that respond differently to the faces of different individuals show that information about the identity of the individual is represented by the responses of a population of neurons, that is, ensemble encoding is used. The rather distributed encoding (within the class faces) about identity in these sensory cortical regions has the advantages of maximising the information in the representation useful for discrimination between stimuli, generalisation, and graceful degradation. In contrast, the more sparse representations in structures such as the hippocampus may be useful to maximise the number of different memories stored. There is evidence that the responses of some of these neurons are altered by experience so that new stimuli become incorporated in the network, in only a few seconds of experience with a new stimulus. It is shown that the representation that is built in temporal cortical areas shows considerable invariance for size, contrast, spatial frequency and translation. Thus the representation is in a form which is particularly useful for storage and as an output from the visual system. It is also shown that one of the representations which is built is view-in-variant, which is suitable for recognition and as an input to associative memory. Another is viewer-centered, which is appropriate for conveying information about gesture. It is shown that these computational processes operate rapidly, in that in a backward masking paradigm, 20–40 ms of neuronal activity in a cortical area is sufficient to support face recognition. In a clinical application of these findings, it is shown that humans with ventral frontal lobe damage have in some cases impairments in face and voice expression identification. These impairments are correlated with and may contribute to the problems some of these patients have in emotional and social behaviour. To help provide an understanding of how the invariant recognition described could be performed by the brain, a neuronal network model of processing in the ventral visual system is described. The model uses a multistage feed-forward architecture, and is able to learn invariant representations of objects including faces by use of a Hebbian synaptic modification rule which incorporates a short memory trace (0.5 s) of preceding activity to enable the network to learn the properties of objects which are spatio-temporally invariant over this time scale.