Emotional cognition without awareness after unilateral temporal lobectomy in humans.
To investigate the function of the amygdala in human emotional cognition, we investigated the electrodermal activity (EDA) in response to masked (unseen) visual stimuli. Six epileptic subjects were investigated after unilateral temporal lobectomy. Emotionally valenced photographic slides (10 negative, 10 neutral) from the International Affective Picture System were presented to their unilateral visual fields under either subliminal or supraliminal conditions. An interaction between hemispheres and emotional valences was found only under the subliminal conditions; greater EDA responses to negative stimuli compared with neutral ones were observed when stimuli were presented to the intact hemispheres. The findings suggest that nonconscious emotional processing is reflected in EDA in a different manner from conscious emotional processing. Medial temporal structures, including the amygdala, thus appear to play a critical role in the neural substrates for this automatic processing. (+info)
The priming method: imaging unconscious repetition priming reveals an abstract representation of number in the parietal lobes.
Most of the current brain imaging methods are limited by the low spatial resolution of neuroimaging techniques and remain unable to measure activity at the scale of single neurons or small columns of neurons, which are the coding elements of the nervous system. In this work we have adapted the priming method, an emerging research strategy that can overcome some of these spatial limitations, to investigate the coding of numerical quantities in the human brain. This approach combines the logic of psychological priming experiments with the recently discovered neurophysiological phenomenon called repetition suppression (RS). In each trial, while subjects perform a constant task, a subliminal prime is presented prior to each target. By varying the relationship between prime and target, one can detect which brain areas present RS specifically for any given level of prime-target repetition. We first expose the general logic, potential and limitations of the priming method and then illustrate it by demonstrating that a region of parietal cortex is coding for numbers at the quantity level, independently of other stimulus attributes, and that this region processes both consciously and unconsciously perceived stimuli. (+info)
Gating of trigemino-facial reflex from low-threshold trigeminal and extratrigeminal cutaneous fibres in humans.
Changes in the size of the test components (R1 and R2) of the trigemino-facial reflex were studied after electrical subliminal conditioning stimulation were applied to the trigeminal, median and sural nerves. After conditioning activation of the trigeminal nerve (below the reflex threshold), the early R1 reflex component showed phasic facilitation, peaking at about 50 ms of interstimulus delay, followed by a long-lasting inhibition recovering at 300-400 ms. The same conditioning stimulation resulted in a monotonic inhibition of the late R2, starting at 15-20 ms, with a maximum at 100-150 ms and lasting 300-400 ms. Intensity threshold for both the R1 and R2 changes ranged from 0.90 to 0.95 times the perception threshold. A similar longlasting inhibition of the R2 reflex response was also seen after conditioning stimulation applied to low-threshold cutaneous afferents of the median and sural nerves. The minimum effective conditioning-test interval was 25-30 ms and 40-45 ms respectively and lasted 600-700 ms. By contrast the early R1 reflex response exhibited a slight long-lasting facilitation with a time course similar to that of the R2 inhibition. The threshold intensity to obtain facilitation of the R1 and inhibition of the R2 test responses after conditioning volley in the median and sural nerves was similar and ranged from 0.9 to 1.2 times the perception threshold. These results demonstrate that low-threshold cutaneous afferents from trigeminal and limb nerves exert powerful control on trigeminal reflex pathways, probably via a common neural substrate. There is evidence that, in addition to any post-synaptic mechanism which might be operating, presynaptic control is a primary factor contributing to these changes. (+info)
Processing of the arousal of subliminal and supraliminal emotional stimuli by the human amygdala.
The amygdala is known to play an important role in conscious and unconscious processing of emotional and highly arousing stimuli. Neuroanatomical evidence suggests that the amygdala participates in the control of autonomic responses, such as skin conductance responses (SCRs), elicited by emotionally salient stimuli, but little is known regarding its functional role in such control. We investigated this issue by showing emotional visual stimuli of varying arousal to patients with left (n = 12), right (n = 8), and bilateral (n = 3) amygdala damage and compared their results with those from 38 normal controls. Stimuli were presented both subliminally (using backward masking) and supraliminally under lateralized presentation to one visual hemifield. We collected SCRs as a physiological index of emotional responses. Subjects subsequently rated each stimulus on valence and arousal under free viewing conditions. There were two key findings: (1) impaired overall SCR after right amygdala damage; and (2) impaired correlation of SCR with the rated arousal of the stimuli after left amygdala damage. The second finding was strengthened further by finding a positive correlation between the evoked SCR magnitude and postsurgery amygdala volume, indicating impaired autonomic responses with larger tissue damage. Bilateral amygdala damage resulted in severe impairments on both of the above measures. Our results provide support for the hypothesis that the left and right amygdalae subserve different functions in emotion processing: the left may decode the arousal signaled by the specific stimulus, whereas the right may provide a global level of autonomic activation triggered automatically by any arousing stimulus. (+info)
The basal ganglia and inhibitory mechanisms in response selection: evidence from subliminal priming of motor responses in Parkinson's disease.
Subliminal response priming was used to investigate inhibitory control processes relevant to response selection impairments in Parkinson's disease. Using a backward masking technique, covert activation of left- or right-hand responses was induced without subjects consciously perceiving the stimuli (right- or left-pointing arrows). The masked priming stimuli were followed by visible arrow stimuli, instructing for a left- or right-hand response, at a delay (interstimulus interval, ISI) of 0 or 100 ms. Motor cortex activation was recorded by means of the electroencephalographic lateralized readiness potential (LRP). Parkinson's disease patients (n = 12) were compared with age-matched controls (n = 12) and young controls (n = 10). In young controls, the ISI = 100 ms task effectively invoked inhibition of the subliminally primed responses, as demonstrated by a reversal of prime-target compatibility effects compared with the ISI = 0 ms task. This reversal implied that there was a so-called negative compatibility effect with faster responses and fewer errors when prime and target arrows pointed in opposite directions than when they required the same response. This negative compatibility effect turned into a positive compatibility effect in Parkinson's disease patients, while age-matched controls produced intermediate values. Together, these results support the view that response selection involves competitive, mutually inhibitory interactions between response alternatives, influenced by basal ganglia-thalamocortical mechanisms. As indicated by the reduced inhibition of partially activated responses, Parkinson's disease and, to a lesser degree, normal ageing affect the efficiency of these inhibitory interactions. (+info)
Absence of increasing cortical fMRI activity volume in response to increasing visceral stimulation in IBS patients.
Cerebral cortical activity associated with perceived visceral sensation represents registration of afferent transduction and cognitive processes related to perception. Abnormalities of gut sensory function can involve either or both of these processes. Cortical registration of subliminal viscerosensory signals represents cerebral cortical activity induced by stimulation of intestinal sensory neurocircuitry without the influence of perception-related cortical activity, whereas those associated with perception represent both neural circuitry and cognitive processes. Our aims were to determine and compare quantitatively cerebral cortical functional magnetic resonance imaging (fMRI) activity in response to subliminal, liminal, and nonpainful supraliminal rectal distension between a group of irritable bowel syndrome (IBS) patients and age/gender-matched controls. Eight female IBS patients and eight age-matched healthy female control subjects were studied using brain fMRI techniques. Three barostat-controlled distension levels were tested: 1) 10 mmHg below perception (subliminal), 2) at perception (liminal), and 3) 10 mmHg above perception (supraliminal). In control subjects, there was a direct relationship between stimulus intensity and cortical activity volumes, ie., the volume of fMRI cortical activity in response to subliminal (3,226 +/- 335 microl), liminal (5,751 +/- 396 microl), and supraliminal nonpainful stimulation (8,246 +/- 624 microl) were significantly different (P < 0.05). In contrast, in IBS patients this relationship was absent and fMRI activity volumes for subliminal (2,985 +/- 332 microl), liminal (2,457 +/- 342 microl), and supraliminal nonpainful stimulation (2,493 +/- 351 microl) were similar. Additional recruitment of cortical fMRI activity volume in response to increasing stimulation from subliminal to liminal and supraliminal domains is absent in IBS patients, suggesting a difference in the processing of perceived stimulation compared with controls. (+info)
Subliminal attentional modulation in crowding condition.
In the crowding phenomenon, recognition of a visual target is impaired by other similar visual stimuli (distracters) presented near the target. This effect may be due largely to insufficient resolution of spatial attention. We showed that attention could subliminally enhance orientation selective adaptation to illusory lines in the crowding condition where target-distractor separation is beyond the limit of spatial resolution of attention. Despite the traditionally held close link between attention and awareness, here we provided evidence for subliminal attentional modulation for orientation stimuli that could not have been consciously perceived. (+info)
Attentional biases to pain and social threat in children with recurrent abdominal pain.
OBJECTIVES: To test whether children with recurrent abdominal pain (RAP) exhibit subliminal (nonconscious) and supraliminal (conscious) attentional biases to pain-related words, and to determine correlates of these biases. Previous research indicates that individuals attend to disorder-relevant threat words, and in this study, attentional biases to disorder-relevant threat (pain), alternative threat (social threat), and neutral words were compared. METHODS: Participants were 59 children with RAP who completed a computer-based attentional bias task. Participants and their parents also completed questionnaires measuring pain, somatic complaints, anxiety/depression, and body vigilance. RESULTS: Children with RAP showed attentional biases toward subliminal pain-related words and attentional biases away from supraliminal pain-related words. Participants' attentional biases to social threat-related words were marginally significant and also reflected subliminal attention and supraliminal avoidance. Attentional biases were related to parent and child reports of pain, body vigilance, and anxiety/depression. CONCLUSIONS: Children with RAP show nonconscious attention to and conscious avoidance of threat-related words. Their attentional biases relate to individual differences in symptom severity. Implications for models of pediatric pain and future studies are discussed. (+info)