Biomedical subjects

Ian J Kirk

Publications and source records attributed to Ian J Kirk.

At least 19 recordsLinked to original sources

PubMed2006

Decreased desychronisation during self-paced movements in frequency bands involving sensorimotor integration and motor functioning in Parkinson's disease.

This study examined sensorimotor integration and motor functioning in seven patients with Parkinson's disease (PD) who had mild symptoms, and seven age-matched controls. Neuro-oscillations were recorded by high-density 128-channel electroencephalography (EEG). Participants were required to perform two tasks: simple tapping of the index finger and thumb and a complex Luria finger apposition task. Both tasks were performed unimanually and bimanually. There were no significant group differences in the task-related power (TRPow) within alpha 1 (mu1) or in beta 1 frequencies (beta1). In contrast, there were significant group differences in the alpha 2 (mu2) and beta 2 frequencies (beta2). Patients had less desychronisation than controls at the electrodes covering the central regions of the scalp. Alpha 2 and beta 2 frequencies have been associated with task-specific sensorimotor integration and motor function, respectively. This activity difference in patients with Parkinson's disease may be due to deficits in sensorimotor integration.

Aged↗

PubMed2006

Volition and the idle cortex: beta oscillatory activity preceding planned and spontaneous movement.

Prior to the initiation of spontaneous movement, evoked potentials can be seen to precede awareness of the impending movement by several hundreds of milliseconds, meaning that this recorded neural activity is the result of unconscious processing. This study investigates the neural representations of impending movement with and without awareness. Specifically, the relationship between awareness and 'idling' cortical oscillations in the beta range (18-24Hz) was assessed. It was found that, in situations where there was awareness of the impending movement, pre-movement evoked potentials were associated with a decrease in beta range oscillations. In contrast, when awareness of the impending movement was not present, the onset of the pre-movement potential was associated with tonic levels of beta range oscillations. A model is considered where by distributed neural activity remains outside of conscious awareness through the persistence of tonic slow wave cortical oscillations.

Adult↗

PubMed2006

Kinesthetic but not visual imagery assists in normalizing the CNV in Parkinson's disease.

OBJECTIVE: This study investigated whether kinesthetic and/or visual imagery could alter the contingent negative variation (CNV) for patients with Parkinson's disease (PD). METHODS: The CNV was recorded in six patients with PD and seven controls before and after a 10min block of imagery. There were two types of imagery employed: kinesthetic and visual, which were evaluated on separate days. RESULTS: The global field power (GFP) of the late CNV did not change after the visual imagery for either group, nor was there a significant difference between the groups. In contrast, kinesthetic imagery resulted in significant group differences pre-, versus post-imagery GFPs, which was not present prior to performing the kinesthetic imagery task. In patients with PD, the CNV amplitudes post-, relative to pre-kinesthetic imagery, increased over the dorsolateral prefrontal regions and decreased in the ipsilateral parietal regions. There were no such changes in controls. CONCLUSIONS: A 10-min session of kinesthetic imagery enhanced the GFP amplitude of the late CNV for patients but not for controls. SIGNIFICANCE: While the study needs to be replicated with a greater number of participants, the results suggest that kinesthetic imagery may be a promising tool for investigations into motor changes, and may potentially be employed therapeutically, in patients with Parkinson's disease.

Aged↗

PubMed2006

Bilateral disadvantage: lack of interhemispheric cooperation in schizophrenia.

Language anomalies and left-hemisphere dysfunction are commonly reported in schizophrenia. Additional evidence also suggests differences in the integration of information between the hemispheres. Bilateral gain is the increase in accuracy and decrease in latency that occurs when identical information is presented simultaneously to both hemispheres. This study measured bilateral gain in controls (n=20) and individuals with schizophrenia (n=10) using a lexical-decision task where word or non-word judgements were made to letter strings presented in the left visual field (LVF), right visual field (RVF) or bilaterally (BVF). Language was not abnormally lateralized in the schizophrenia group. Controls exhibited the expected decrease in latency when words were presented bilaterally. This effect was not observed in the schizophrenia group who were actually disadvantaged in this condition. The lack of bilateral gain in schizophrenia is discussed as arising from differences in the connections between areas in each hemisphere that mediate language.

Adult↗

PubMed2006

Spatial frequency-specific potentiation of human visual-evoked potentials.

Recent research has suggested that cortical long-term potentiation can be induced non-invasively in humans by using rapid visual stimulation. The present study extends these findings by investigating the specificity of this long-term potentiation effect to the inducing stimulus. One group of study participants were tetanized using a one cycle-per-degree sine grating, while a second group was tetanized using a five cycles-per-degree sine grating. Using electroencephalography, we found that an increase in the N1b potential was specific to sine gratings of the same frequency as the tetanus. No effect was observed in the N1b for sine gratings of a different spatial frequency. These results suggest that the long-term potentiation effect induced by the sensory tetanus is isolated to a discrete neural population in the visual cortex.

Adult↗

PubMed2006

Temporal dynamics of masked word reading.

The repercussions of unconscious priming on the neural correlates subsequent cognition have been explored previously. However, the neural dynamics during the unconscious processing remains largely uncharted. To assess both the complexity and temporal dynamics of unconscious cognition the present study contrasts the evoked response from classes of masked stimuli with three different levels of complexity; words, consonant strings, and blanks. The evoked response to masked word stimuli differed from both consonant strings and blanks, which did not differ from each other. This response was qualitatively different to any evoked potential observed when stimuli were consciously visible and peaked at 140ms, earlier than is usually associated with differences between words and strings and 100ms earlier than word-consonant string differences in the visible condition. The evoked response demonstrates a qualitatively distinct signature of unconscious cognition and directly demonstrates the extraction of abstract information under subliminal conditions.

Adult↗

PubMed2006

Long-term enhanced desynchronization of the alpha rhythm following tetanic stimulation of human visual cortex.

It had been shown previously that a photic tetanus induces LTP-like changes in the visual cortex, as indexed by an enhancement of the N1b component of the visual evoked potential, recorded non-invasively by electroencephalography. This potentiation was shown to last over 1 h. In the present study, the effect of a photic tetanus on oscillatory activity is investigated. EEGs were collected from eight healthy subjects in three conditions while visual checkerboards were displayed. Following baseline presentations in two conditions a lateralized visual tetanus was given, either to the left or right visual field, and in a third condition no tetanus was given. This was followed by a return to baseline presentations, both immediately after the tetanus/control block, and 1 h later. Enhanced event-related desynchronization (ERD) of the alpha rhythm lasting 1 h was seen following the photic tetanus over occipital electrodes. Because ERD of the alpha rhythm is thought to represent active cortex, these results suggest that the visual tetanus induces long-lasting cortical changes, with stronger neuronal assemblies and increased neuronal output.

Adult↗

PubMed2005

Effects of long-term potentiation in the human visual cortex: a functional magnetic resonance imaging study.

Applying functional magnetic resonance imaging techniques, hemodynamic responses elicited by slowly flashing checkerboards (0.25 Hz) were measured both before and after a block of rapidly presented checkerboards (9 Hz -- a 'photic tetanus') was delivered. It has been shown previously, using electroencephalography, that this photic tetanus potentiates components of the visual-evoked potential. In the present study, hemodynamic responses in the extrastriate visual cortex were significantly increased to checkerboards presented at a low frequency after the administration of the photic tetanus. These results support the idea that long-term potentiation can be demonstrated non-invasively within the human visual cortex and provide evidence that the plastic changes are localized within the secondary visual cortex.

Brain Mapping↗

PubMed2005

The neurophysiological correlates of face processing in adults and children with Asperger's syndrome.

Past research has found evidence for face and emotional expression processing differences between individuals with Asperger's syndrome (AS) and neurotypical (NT) controls at both the neurological and behavioural levels. The aim of the present study was to examine the neurophysiological basis of emotional expression processing in children and adults with AS relative to age- and gender-matched NT controls. High-density event-related potentials were recorded during explicit processing of happy, sad, angry, scared, and neutral faces. Adults with AS were found to exhibit delayed P1 and N170 latencies and smaller N170 amplitudes in comparison to control subjects for all expressions. This may reflect impaired holistic and configural processing of faces in AS adults. However, these differences were not observed between AS and control children. This may result from incomplete development of the neuronal generators of these ERP components and/or early intervention.

Adolescent↗

PubMed2005

Symmetry of callosal information transfer in schizophrenia: a preliminary study.

OBJECTIVE: While there is much evidence to suggest left hemisphere dysfunction and interhemispheric transfer deficits in schizophrenia, the right hemisphere is rarely implicated. This study uses 128-channel EEG to assess whether asymmetry of interhemispheric transfer found in normal individuals is present in those with schizophrenia, and whether this might point to a right-hemisphere dysfunction. METHODS: Simple reaction time (RT) was recorded to stimuli presented to the left visual field (LVF), right visual field (RVF) or bilaterally (BVF) in 13 males with schizophrenia and 13 controls. 128-Channel EEG was simultaneously recorded. Interhemispheric transfer time (IHTT) in each direction was calculated by comparing the latencies of N160 EP components in the hemispheres contralateral and ipsilateral to stimulation. RESULTS: While controls showed faster information transfer from the right-to-left hemisphere, this asymmetry was not present in the schizophrenia group who also exhibited a concomitant decrease in the amplitude of the N160 in the right hemisphere. CONCLUSIONS: Results are interpreted with reference to a loss of rapidly conducting myelinated axons in the right hemisphere in schizophrenia.

Adult↗

PubMed2005

Lack of asymmetrical transfer for linguistic stimuli in schizophrenia: an ERP study.

OBJECTIVE: To assess the mechanisms underlying lack of speeded information transfer asymmetry (faster right to left) for verbal information in schizophrenia. METHODS: Interhemispheric transfer times (IHTT) between the hemispheres were assessed using a lateralized lexical-decision task in males with schizophrenia (N = 12) and matched controls (N = 12). Words were presented to the left visual field (LVF), right visual field (RVF), or bilaterally (BVF) while 128-channel EEG was recorded continuously. A direct measure of IHTT in each direction was obtained by comparing the latencies of the N160 evoked potential (EP) component in the hemispheres contralateral and ipsilateral to stimulation. RESULTS: Controls showed faster information transfer from the right to left hemisphere (R-to-L) for linguistic stimuli. The two groups did not differ for IHTTs L-to-R. Lack of IHTT asymmetry in the schizophrenia groups was associated with an overall concomitant decrease in the amplitude of the N160 in the right hemisphere. CONCLUSIONS: Differences in IHTT asymmetry may be attributed to lack of right hemisphere activation and not callosal dysfunction as has been previously suggested. SIGNIFICANCE: It is suggested that a relative excess of myelinated axons in the right hemisphere speeds IHTT faster R-to-L, findings are discussed with reference to differences in right hemisphere white matter connectivity in schizophrenia.

Adult↗

PubMed2005

Early visual evoked potentials in callosal agenesis.

Three participants with callosal agenesis and 12 neurologically normal participants were tested on a simple reaction time task, with visual evoked potentials collected using a high-density 128-channel system. Independent-components analyses were performed on the averaged visual evoked potentials to isolate the components of interest. Contrary to previous research with acallosals, evidence of ipsilateral activation was present in all 3 participants. Although ipsilateral visual components were present in all 4 unilateral conditions in the 2 related acallosal participants, in the 3rd, these were present only in the crossed visual field-hand conditions and not in the uncrossed conditions. Suggestions are made as to why these results differ from earlier findings and as to the neural mechanisms facilitating this ipsilateral activation.

Adult↗

PubMed2005

Right hemispheric dysfunction in schizophrenia.

This study uses the Poffenberger (1912) paradigm, which compares the difference between "crossed" (stimuli and motor response areas are contralateral) and "uncrossed" (stimuli and motor response areas are ipsilateral) conditions to estimate interhemispheric transfer time. Simple reaction time (RT) was recorded to stimuli presented to the left visual field (LVF), right visual field (RVF), or bilaterally (BVF) in individuals with schizophrenia (n = 10) and controls (n = 14), who responded using either the left or right hand. While the results provide no evidence for differences between the groups in information transfer between the hemispheres, the schizophrenia group were significantly slower to respond to LVF stimuli, suggesting right hemisphere dysfunction.

Brain↗

PubMed2005

Long-term potentiation of human visual evoked responses.

Long-term potentiation (LTP) is a candidate synaptic mechanism underlying learning and memory that has been studied extensively at the cellular and molecular level in laboratory animals. To date, LTP has only been directly demonstrated in humans in isolated cortical tissue obtained from patients undergoing surgery, where it displays properties identical to those seen in non-human preparations. Inquiry into the functional significance of LTP has been hindered by the absence of a human model. Here we give the first demonstration that the rapid repetitive presentation of a visual checkerboard (a photic 'tetanus') leads to a persistent enhancement of one of the early components of the visual evoked potential in normal humans. The potentiated response is largest in the hemisphere contralateral to the tetanized visual hemifield and is limited to one component of the visual evoked response (the N1b). The selective potentiation of only the N1b component makes overall brain excitability changes unlikely and suggests that the effect is due instead to an LTP process. While LTP is known to exist in the human brain, the ability to elicit LTP from non-surgical patients will provide a human model system allowing the detailed examination of synaptic plasticity in normal subjects and may have future clinical applications in the assessment of cognitive disorders.

Adult↗

PubMed2004

Influence of task complexity on manual asymmetries.

The degree of manual asymmetry is generally assumed to vary with task complexity. However, task complexity as a factor in manual asymmetries has rarely been examined directly. Further, the results of psychophysical studies indicate that manual asymmetry increases with task complexity, while physiological studies consistently report a reduction of manual asymmetries in more complex tasks. The use of different tasks (rather than different complexity levels within a given task) in many psychophysical studies might result in this inconsistency. This study investigated the influence of task complexity on manual asymmetries in 70 right-handed subjects. We used three complexity levels within a finger-tapping paradigm. A strong advantage of the preferred hand was particularly pronounced in the simple finger-tapping task. When the task was more complex, the advantage of the preferred hand, and thus, the manual asymmetry significantly decreased or disappeared. These results support previous suggestions that simple motor tasks involve localised neural networks confined to one cerebral hemisphere, while complex motor tasks are controlled by more widely distributed neuronal assemblies that involve both hemispheres. However, the influence of task complexity on manual asymmetry seems not to be monotonic.

Analysis of Variance↗

PubMed2003

Age-related improvements in auditory temporal resolution in reading-impaired children.

Individuals with developmental dyslexia show impairments in processing that require precise timing of sensory events. Here, we show that in a test of auditory temporal acuity (a gap-detection task) children ages 6-9 years with dyslexia exhibited a significant deficit relative to age-matched controls. In contrast, this deficit was not observed in groups of older reading-impaired individuals (ages 10-11 years; 12-13 years) or in adults (ages 23-25 years). It appears, therefore, that early temporal resolution deficits in those with reading impairments may significantly ameliorate over time. However, the occurrence of an early deficit in temporal acuity may be antecedent to other language-related perceptual problems (particularly those related to phonological processing) that persist after the primary deficit has resolved. This result suggests that if remedial interventions targeted at temporal resolution deficits are to be effective, the early detection of the deficit and early application of the remedial programme is especially critical.

Adult↗

PubMed2003

Anterior-posterior beta asymmetries in dyslexia during lexical decisions.

High-density EEG was recorded in 12 compensated dyslexics, 6 classified as dysphonetic and 6 as dyseidetic, and in 12 matched controls while they carried out a lexical-decision task. Relative to normal controls, dysphonetics showed higher beta power in anterior relative to posterior regions, while dyseidetics showed higher beta power in posterior relative to anterior regions. Further, controls (but not dyslexics) showed a positive correlation between performance on the task and the ratios of both left-to-right and anterior-to-posterior beta asymmetry. According to the dual-route theory of reading, there are two strategies that can be used in lexical decision: A visual strategy involving visual word identification and direct access to a visual lexicon, and a phonological strategy involving grapheme-to-phoneme conversion and access to a speech output lexicon. Our results therefore suggest compensation through weakness rather than strength, with phonological dyslexics focusing on a grapheme-to-phoneme strategy and dyseidetics focusing on visual word identification.

Adult↗

PubMed2002

Impaired dodging in food-conflict following fimbria-fornix transection in rats: a novel hippocampal formation deficit.

It is well known that damage to the hippocampal formation (Ammon's horn, dentate gyrus, fimbria-fornix, and other pathways) produces impairments in spatial navigation and in certain forms of learning. Lesions within these structures have also been reported to produce some motor impairments, but the nature of these impairments is less understood. The present study examined the effects of fimbria-fornix lesions on food wrenching and dodging, social interactions that occur when one rat attempts to steal food from a conspecific, who in turn attempts to protect the food by an evasive movement. Lesion effectiveness was confirmed histologically and electrophysiologically, by the loss of hippocampal rhythmical slow-wave activity (RSA or theta), and by changes in open field behavior (increased open field behavior, less thigmotaxis and more defecation). Analysis of the social interaction indicated when an eating control rat was approached by a conspecific that was attempting to steal its food, it prevented the theft by dodging, a rapid lateral maneuver involving forequarter turning and stepping with the rear limbs. Rats with fimbria-fornix lesions were significantly impaired in dodging and so were more likely to lose their food to the robber. This novel deficit in motor behavior is discussed in relation to contemporary theories of hippocampal function and it is suggested that the deficit may be caused by an inability of the fimbria-fornix damaged animals to disengage attention from eating in order to initiate an evasive movement to protect food. The finding of this novel deficit underscores the importance of considering both loss as well as release phenomena in the analysis of hippocampal formation function.

Agonistic Behavior↗