Kajian pengimejan resonans magnet kefungsian (fMRI) subjek tunggal ini menyelidiki kesan daya dan laju tepikan ke atas sifat pengaktifan korteks berkaitan motor semasa tepikan jari rentak sendiri secara bilateral. Subjek melakukan empat cara tepikan jari rentak sendiri iaitu sentuh-perlahan (SP), sentuh-laju (SL), tekan-perlahan (TP) dan tekan-laju (TL) dalam satu imbasan fMRI. Model linear am (GLM) digunakan dalam penjanaan pengaktifan otak. Pentaakulan statistik kemudiannya dibuat mengenai pengaktifan otak menggunakan teori medan rawak (RFT) Gaussian pada aras keertian diperbetulkan (α = 0.05), dengan andaian tiada pengaktifan berlaku. Keputusan mendapati otak mengkoordinasi tepikan jari bilateral rentak sendiri dengan penglibatan korteks berkaitan motor iaitu girus presentral (PCG) bilateral, serebelum bilateral dan juga kawasan motor tambahan (SMA). Peningkatan daya tepikan menonjolkan pengaktifan yang bererti (p < 0.05 diperbetulkan) pada PCG bilateral (Kawasan Brodmann (BA) 6) sejajar dengan fungsinya dalam mencetus tindakan motor seperti mengawal daya tepikan. Peningkatan laju tepikan pula menyebabkan peningkatan pengaktifan otak secara bererti (p < 0.05 diperbetulkan) hanya pada korteks kesatuan somatoderia iaitu pada lobus parietal superior (SPL) kanan atau BA7 kanan. Ini mencadangkan bahawa SPL memainkan peranan penting dalam mengkoordinasi pergerakan berkemahiran terancang.
Samples of Mn0.6-zMgzZn0.4Fe2O4 ferrites (z = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) were prepared by solid state reaction. X-ray diffraction (XRD) confirmed the formation of a single phase spinel structure. Analysis of XRD data indicates that the lattice parameter (a) and XRD density (ÏXRD) decrease with the substitution of Mn by Mg. This ferrite system indicates a maximum magnetization at a certain composition of Mg. The initial permeability (µi) increases for samples with higher magnetization, while the coercivity vary in the opposite manner. DC resistivity (Ï) at 300 K was obtained for annealed an unannealed samples. It is seen that the resistivities at 300 K for samples with z = 0.3, 0.4, 0.5 and 0.6 are lower than the others. The electrical resistivity as a function of temperature in one complete cycle (300 K---680 K---300 K) for unannealed samples indicates anomalies at Neel temperature (TN) and around a certain temperature (Tot). Anomaly at Tot can be seen during heating run and is greater for samples with higher Mg content. The anomaly is absent during cooling run and for the annealed samples except for Z = 0.6. The existence of this anomaly is discussed as due to a contribution of conductivity from the tetrahedral sites and cation redistribution between the two interstitial A and B sites. TN was determined from the variation of resistivity with temperature for the anealed samples and is seen to increase with increasing Mg content. The ferrimagnetic activation energy (Ef) is smaller than the paramagnetic activation energy (Ep) for all samples.
Sistem ferit Mn0.6-zMgzZn0.4Fe2O4 (z = 0, 0.1, 0.2, 0.3, 0.4, 0.5 dan 0.6) disediakan melalui kaedah tindakbalas keadaan pepejal. Pembelauan sinar-X (XRD) mengesahkan kesemua sampel berstruktur spinel fasa tunggal. Analisa data XRD menunjukkan pemalar kekisi (a) dan ketumpatan XRD (rXRD) yang berkurang dengan penggantian Mn oleh Mg. Sistem ferit ini menunjukkan pemagnetan maksimum pada suatu komposisi Mg. Kebolehtelapan awal (µi) meningkat bagi sampel dengan pemagnetan yang tinggi manakala koersiviti (Hc) berubah sebaliknya. Kerintangan elektrik arus terus (Ïat) pada 300 K diukur untuk sampel yang disepuh lindap dan yang tidak disepuh lindap. Nilai kerintangan elektrik pada 300 K untuk sampel dengan z = 0.3, 0.4, 0.5 dan 0.6 didapati lebih rendah berbanding dengan yang lain. Perubahan kerintangan elektrik terhadap suhu dalam satu kitar (300 K---680 K---300 K) bagi sampel yang tidak disepuh lindap menunjukkan anomali pada suhu Neel (TN) dan suatu anomali di sekitar suatu suhu (Tot). Anomali pada Tot dicerap semasa pengukuran suhu meningkat dan semakin jelas untuk sampel dengan kandungan Mg yang tinggi. Anomali tersebut lenyap untuk pengukuran suhu menurun dan pengukuran bagi sampel yang disepuh lindap kecuali untuk z = 0.6. Kewujudan anomali tersebut dibincangkan sebagai berpunca daripada sumbangan kekonduksian pada tapak tetrahedron dan taburan semula kation-kation di antara dua tapak interstis A dan B. TN ditentukan daripada lengkung kerintangan melawan suhu untuk sampel yang disepuh lindap dan didapati meningkat dengan kandungan Mg. Kesemua sampel menunjukkan tenaga pengaktifan ferimagnet (Ef) yang lebih kecil daripada tenaga pengaktifan paramagnet (Ep ).
The electrical resistivity of Mg0.6Zn0.4Fe2O4 ferrite was measured as a function of temperature in the range 300-630 K. Two anomalies are observed in the resistivity curves for measurements during heating up. These anomalies are identified as a magnetic anomaly at the Neel temperature, TN = 598 K, while the other one at TOt = 445 K is discussed as due to the contribution of conduction from the tetrahedral sites. The anomaly at Tot was reduced in the measurements during recooling, while the anomaly at TN was disappeared completely during recooling and second cycle. These effects are discussed as due to the increase of Fe2+ ions at the octahedral sites as a result of cation redistribution at higher temperatures. A relatively small anomaly at Tot still can be observed during the second run. This is possible if the Fe2+ ions have a preference to be relocated at the tetrahedral sites at lower temperatures.
Kerintangan elektrik Mg0.6Zn0.4Fe2O4 ferit telah diukur sebagai fungsi suhu dalam julat 300 - 630 K. Dua anomali dapat dicerap pada lengkung kerintangan bagi pengukuran semasa pemanasan. Dua anomali tersebut dikenalpasti sebagai anomali magnet pada suhu Neel, TN = 598 K, manakala yang satu lagi pada Tot = 445 K dibincangkan sebagai berpunca daripada sumbangan kekonduksian pada tapak tetrahedron. Anomali pada Tot mengurang dalam pengukuran semasa penyejukan semula pada julat suhu yang sarna, manakala anomali pada TN terus lenyap dalam pengukuran semasa penyejukan semula dan juga semasa kitar kedua. Kesan ini dibincangkan sebagai disebabkan oleh peningkatan ion Fe2+ pada tapak oktahedron daripada proses taburan semula kation pada suhu tinggi. Anomali yang berkurang pada Tot masih boleh dicerap semasa pengukuran kitar kedua. Keadaan seperti ini adalah mungkin jika ion Fe2+ mempunyai kecenderongan untuk bertempat semula pada tapak tetrahedron apabila suhu menurun.
The a.c. electrical response of a polycrystalline Li0.25Ni0.2Zn0.3Fe2.25O4 ferrite is studied by means of impedance spectroscopy. The impedance measurement was performed at different input voltage amplitudes in ten decades of frequency (1 mHz - 10 MHz). Two overlapping semicircles with negative capacitance phenomenon below 1 Hz are observed at all amplitudes. The two semicircles are mainly attributed to the grain and grain boundary processes at high and low frequencies respectively. The grain boundary impedance shows a non-linear dependence on the input voltage, where the corresponding impedance semicircle is smaller for larger amplitude. However, a linear response is observed for the grain component. The dependence of the a.c. electrical properties of the grain and grain boundary components on the amplitude of the input voltage is discussed.
Ransangan elektrik a.u. daripada ferit Li0.25Ni0.2Zn0.3Fe2.25O4 berpolihablur dikaji dengan menggunakan spektroskopi impedans. Pengukuran impedans dilakukan pada beberapa amplitud voltan masukan dalam julat sepuluh dekad frekuensi (1 mHz - 10 MHz). Dua lengkung separuh bulatan yang bertindih dengan fenomena kapasitans negatif di bawah frekuensi 1 Hz dapat diperhatikan pada setiap nilai amplitud. Kedua-dua lengkung separuh bulatan tersebut berpunca daripada proses-proses butiran dan sempadan butiran masing-masing pada frekuensi tinggi dan rendah. Impedans sempadan butiran menunjukkan persandaran tak-linear ke atas voltan masukan, dengan separuh bulatan impedans yang berpadanan yang mengecil dengan peningkatan amplitud. Akan tetapi, suatu ransangan linear dapat diperhatikan bagi komponen butiran. Kebergantungan sifat elektrik a.u. bagi komponen-Âkomponen butiran dan sempadan butiran kepada amplitud voltan masukan dibincangkan.
Kajian garis pangkal pengimejan resonans magnet kefungsian (fMRI) telah dijalankan di Jabatan Radiologi, Hospital Universiti Kebangsaan Malaysia ke atas seorang subjek lelaki sihat berumur 25 tahun menggunakan sistem pengimejan resonans magnet (MRI) 1.5 T. Kajian ini menggunakan gerakan jari tangan kanan dan kiri untuk merangsang aktiviti neuron di dalam korteks serebrum. Subjek diarahkan supaya menekan jari-jari pada ibu jari secara bergilir-gilir semasa imbasan kefungsian dilakukan. Paradigma 5 kitar aktifrehat digunakan dengan setiap kitar masing-masing mengandungi 20 siri pengukuran. Keputusan menunjukkan bahawa rantau otak yang aktif akibat gerakan jari adalah girus presentral merangkumi kawasan motor primer. Pengaktifan otak adalah secara kontralateral terhadap gerakan jari tangan kanan dan kiri. Keamatan isyarat keadaan aktif didapati lebih tinggi daripada keamatan isyarat keadaan rehat. Analisis yang dilakukan ke atas beberapa rantau pengaktifan yang diminati (ROI) pada beberapa hirisan menunjukkan perbezaan yang bererti (p < 0.05) antara keamatan keadaan aktif dan rehat untuk nilai ambang statistik (Z) = 1.0 dan 1.5. Perbezaan purata antara kedua-dua purata keamatan isyarat keadaan aktif dan rehat pada manamana hirisan untuk kedua-dua nilai Z menunjukkan magnitud pengaktifan yang lebih tinggi pada hemisfera kanan otak iaitu apabila subjek menggerakkan tangan kirinya. Bilangan voksel yang aktif juga didapati lebih tinggi pada hemisfera kanan berbanding pada hemisfera kiri otak. Keputusan ini menyokong fakta bahawa bagi subjek yang tidak kidal, kawasan pengaktifan motor pada hemisfera kanan otak semasa gerakan jari tangan kiri mengalami rangsangan hemodinamik yang lebih tinggi berbanding dengan hemisfera kiri otak semasa gerakan jari tangan kanan. Fenomena rangsangan hemodinamik yang diperhatikan dalam kajian ini dibincangkan berdasarkan kepada kebergantungan kontras isyarat kepada aras oksigen darah (BOLD).
Kajian garis pangkal pengimejan resonans magnet kefungsian (fMRI) telah dijalankan ke atas 2 orang subjek lelaki sihat (kidal dan tidak kidal) masing-masing berumur 22 dan 25 tahun. Imbasan fMRI dijalankan menggunakan sistem pengimejan resonans magnet (MRI) 1.5 T di Jabatan Radiologi, Hospital Universiti Kebangsaan Malaysia. Kajian ini menggunakan gerakanjari tangan kanan dan kiri untuk merangsang aktiviti neuron di dalam korteks serebrum. Paradigma 5 kitar aktifIrehat digunakan dengan setiap kitar mengandungi satu blok aktif dan satu blok rehat yang masing-masing mengandungi 10 siri pengukuran. Imej fMRI dianalisis menggunakan pekej perisian MatLab dan pemetaan statistik berparameter 2 (sPM2). Proses pendaftaran jasad tegar menggunakan penjelmaan afin 6 parameter dilakukan ke atas kesemua imej kefungsian berwajaran T2*. Keputusan menunjukkan bahawa pergerakan subjek adalah minimum sama ada dalam arah translasi (< 1 mm) atau putaran (< 1 ). Kesemua imej dinormalkan melalui proses peledingan tak linear menggunakan penjelmaan afin 12 parameter dan didapati sepadan dengan pencontoh yang telahpun mematuhi ruang anatomi piawai. Walau bagaimanapun, bentuk, resolusi dan kontras imej kefungsian telah berubah sedikit berbanding dengan imej asal. Pelicinan imej menggunakan kernel Gaussian isotropik 6 mm menyebabkan data imej lebih bersifat parametrik dengan kehilangan yang ketara dalam resolusi dan kontras. Pengasingan struktur yang dilakukan ke atas imej berwajaran T1 mengklaskan tisu otak kepadajirim kelabu, jirim putih dan bendalir serebrospina. Pasca pemprosesan ruang bagi imej kefungsian dan struktur menjadikan data imej bersifat parametrik dengan taburan jenis Gaussian dan sedia untuk dianalisis menggunakan model linear am dan teori medan rawak Gaussian.
A functional magnetic resonance imaging (fMRI) study was conducted on 4 healthy male and female subjects to investigate brain activation during passive and active listening. Two different experimental conditions were separately used in this study. The first condition requires the subjects to listen to a simple arithmetic instruction (e.g. one-plus-two-plus-three-plus-four) - passive listening. In the second condition, the subjects were given the same series of arithmetic instruction and were required to listen and perform the calculation - active listening. The data were then analysed using the Statistical Parametric Mapping (SPM5) and the MATLAB 7.4 (R2007a) programming softwares. The results obtained from the fixed (FFX) and random effects analyses (RFX) show that the active-state signal intensity was significantly higher (p < 0.05) than the resting-state signal intensity for both conditions. The results also indicate significant differences (p < 0.001) in brain activation between passive and active listening. The activated cortical regions during passive listening, as obtained from the FFX of the first condition is symmetrical in the left and right temporal and frontal lobes covering the cortical auditory areas. However, for the second condition, which was active listening, more activation occurs in the left hemisphere with a reduction in the number of activated voxels and their signal intensity in the right hemisphere. Activation mainly occurs in the middle temporal gyrus, precentral gyrus, middle frontal gyrus, superior temporal gyrus and several other areas in the frontal lobes. The point of maximum signal intensity has been shifted to a new coordinates during active listening. It is also observed that the magnetic resonance signal intensity and the number of activated voxel in the right and left superior temporal lobes for the second condition have been reduced as compared to that of the first condition. The results obtained strongly suggest the existence of functional specialisation. The results also indicate different networks for the two conditions. These networks clearly pertain to the existence of functional connectivity between activation areas during listening and listening while performing a simple arithmetic task.
Kajian garis pangkal pengimejan resonans magnet kefungsian (fMRI) telah dijalankan ke atas 2 orang subjek lelaki sihat dominan tangan kanan dan kiri. Kajian ini menggunakan gerakan jari tangan kanan dan kiri untuk merangsang aktiviti neuron di dalam korteks serebrum. Subjek diarahkan supaya menekan jari-jari pada ibu jari secara bergilir-gilir semasa imbasan fMRI dilakukan. Paradigma 5 kitar aktif-rehat digunakan dengan setiap kitar mengandungi satu blok aktif dan satu blok rehat dengan 10 siri pengukuran untuk setiap blok. Seratus isipadu imej fMRI bagi setiap subjek dianalisis menggunakan pekej perisian MatLab dan SPM2. Model linear am (GLM) digunakan untuk menganggar secara statistik parameter yang mencirikan model rangsangan hemodinamik bagi gerakan jari. Kesimpulan mengenai pengaktifan otak yang diperhatikan dijana secara statistik berasaskan teori medan rawak (RFT) Gaussian. Keputusan menunjukkan bahawa rantau otak yang aktif akibat gerakan jari adalah pada girus presentral merangkumi kawasan motor primer. Pengaktifan otak adalah secara kontralateral terhadap gerakan jari tangan kanan dan kiri. Keamatan isyarat keadaan aktif didapati lebih tinggi secara bererti (p < 0.001) daripada keamatan isyarat keadaan rehat. Bilangan voksel yang aktif didapati lebih tinggi pada hemisfera otak yang mengawal gerakan jari bagi tangan yang tidak dominan untuk kedua-dua subjek. Keputusan ini menyokong fakta bahawa kawasan pengaktifan motor pada hemisfera otak semasa gerakan jari tangan yang tidak dominan mengalami rangsangan hemodinamik yang lebih tinggi dan kawasan pengaktifan yang lebih luas berbanding dengan kawasan pengaktifan pada hemisfera otak yang mengawal gerakan jari bagi tangan yang dominan.
Knowledge about the hemodynamic model that mediates synaptic activity and measured magnetic resonance signal is essential in understanding brain activation. Neural efficacy is a hemodynamic parameter that would change the evoked hemodynamic responses. In this work, brain activation and neural efficacy of the activated brain areas during simple addition task in two different backgrounds were studied using fMRI. The objectives were to determine the activated areas during the performance of arithmetic addition in quiet (AIQ) and noisy (AIN) background and to investigate the relationship between neural efficacy and height extent of activation for the respective areas. Eighteen healthy male participants performed simple arithmetic addition in quiet and in noise. Bilateral cerebellum, superior temporal gyrus (STG), temporal pole (TP) and supplementary motor area (SMA) were significantly (p < 0.05) activated during AIQ and AIN. Left middle frontal gyrus (L-MFG), right superior frontal gyrus (R-SFG), right superior orbital gyrus (R-SOG) and bilateral insula were more active in quiet as compared to in noise while the left middle cingulate cortex (L-MCC), left amygdala (L-AMG), right temporal pole (R-TP) and left cerebellum (L-CER) were more active in noise as compared to in quiet. The t value for most of the activated regions was found to be inversely proportional to the neural efficacy. Significant (p < 0.05) negative relationship between t value and neural efficacy were found for R-STG and bilateral cerebellum during AIQ, while for AIN, similar relationships were found in R-CER, R-STG and R-TP. This study suggests that while being significantly activated, the hemodynamic responses of these brain regions could have been suppressed by the stimulus resulting in an intensity decrease with increasing neural efficacy.
Despite a vast number of studies that were focused on the roles of superior temporal gyrus (STG) and cerebellum as sensory
area, little is known about their involvement in cognitive function such as attention and perception. The present fMRI
study aimed to identify this cognitive role from brain activation profile of STG and cerebellum obtained from an arithmetic
addition task. Eighteen healthy right hand dominance male adults participated in this study. They were instructed to solve
single-digit addition tasks in quiet and noisy background during the fMRI scan. Both the in-quiet and in-noise addition
tasks activated the bilateral STG and cerebellum (lobule VI and lobule VII) significantly but differentially. In both quiet
and noisy conditions, STG activation is dominant in the left hemisphere while cerebellum showed a right hemisphere
dominance. Bilateral STG and cerebellum (lobule VI) activation decreasedin noise, conversely cerebellum (lobule VII)
activation increased in noise. These asymmetrical activation indicated hemispheric lateralization and differential behaviors
of both brain areas in different environment while performing simple arithmetic addition task.
Proses penuaan seringkali dikaitkan dengan kemerosotan sistem kognitif. Kemerosotan tersebut bermula seawal usia dua puluhan dan berterusan secara linear. Walau bagaimanapun, kesan penuaan ke atas ciri kehubungan antara kawasan otak masih belum difahami. Dalam kajian ini, pengimejan resonans magnet kefungsian (fMRI) digunakan untuk mengkaji kesan penuaan ke atas kehubungan otak yang terhasil daripada tugasan mengulang secara terbalik (BRT). Subjek normal dalam empat kumpulan umur iaitu 20-29 tahun (n=14), 30-39 tahun (n=14), 40-49 tahun (n=10) dan 50-65 tahun (n=14) mengambil bahagian dalam kajian ini. Stimulus BRT terdiri daripada satu siri lima perkataan yang diberi secara auditori. Pemetaan statistik berparameter (SPM) dan pemodelan sebab dan akibat dinamik (DCM) digunakan untuk menentukan pengaktifan dan kehubungan otak. Sebanyak 200 model kehubungan intrahemisfera dan 150 interhemisfera dibina bagi menguji kewujudan gandingan antara girus temporal superior (STG), girus Heschl (HG), talamus (TH) dan girus presentral (PCG) kesemua subjek. Keputusan DCM menunjukkan subjek keempat-empat kumpulan umur menggunakan kehubungan intrahemisfera yang sama semasa tugasan BRT. Kehubungan interhemisfera pula didapati berubah menjadi semakin kompleks apabila usia meningkat. Perubahan tersebut didapati bermula pada usia 40 tahun. Keputusan ini menyokong penemuan terdahulu bahawa penuaan menyebabkan perubahan pada sistem neuron otak seterusnya mempengaruhi pemprosesan kognitif.
The complex scattering parameters (S11* and S21*), relative dielectric permittivity (er* = er' - jer"), relative magnetic permeability (mr* = mr' - jmr") and absorption characteristics of some thermoplastic natural rubber (TPNR) – Fe3O4/YIG composites were investigated by means of a microwave vector network analyser and specular absorber method. The measurements were performed in the frequency range of 1 – 13 GHz with and without the presence of a transverse external magnetic field with magnitude of 1 T. The specular absorber method is used in determining the reflection loss (RL) of the composites and its dependence on material properties, thickness and the external magnetic field. In toroidal form, the composites under study seem to transmit more (Pt > 60%) but absorb and reflect less (Pa + Pr < 30%) microwave power in the frequency range used in this study and in both unmagnetised and magnetised states. The external magnetic field is seen to have the effects of reducing S11*, S21*, er', er", mr' and mr". The suppression of the relaxation and resonance behaviours on the mr' and mr" plots for all samples are observed for measurements performed in the presence of the external field. The composites, as revealed by the specular absorber method, show conditions of minimal reflection on RL versus frequency plot for all sample thickness where more than 95% of the microwave power is not reflected back. The location of the dips of minimal reflection on the frequency domain depend on the thickness, the dielectric and magnetic properties of the materials. The conditions of minimal reflection was found to occur when the thickness (t) of the sample equals the odd number multiple of a quarter wavelength in the material (lm), t = nlm/4 (n = 1, 3, 5, 7 …), where a geometrical cancellation took place at the surface of the absorber between the reflected waves, resembling a thin filem inteference phenomenon. The dips are suppressed and shifted to a higher frequency in the presence of the external magnetic field. With the knowledge of the dielectric permittivity and magnetic permeability of a material, the specular absorber method may provides a simple theoretical graphic aids in determining the absorption characteristics and location of the matching condition in the frequency domain.
Inferior parietal lobule (IPL) and inferior temporal gyrus (ITG) are two important brain regions for the default mode
network (DMN). IPL has been known to be involved in the control of attention and responding to given information while
ITG is involved in the processing and perception awakened by visual stimuli. These two key DMN regions are highly
interconnected as determined from white matter and fiber tracking studies. However, little is known about their nature
of connectivity while the brain is at rest, whether it is linear, bilinear or nonlinear and whether it is of mono- or bidirection. Resting state functional magnetic resonance imaging (rsfMRI) data were obtained from 7 healthy male and
female participants (average age = 20.7 ± 4.5 years) and were concatenated. Data were analyzed using statistical
parametric mapping (SPM12). Endogenous brain signals were modelled by Fourier series at 0.01 – 0.08 Hz. IPL-ITG
connected linear, bilinear and non-linear causal models in both hemispheres were constructed and estimated by means of
stochastic dynamic causal modelling (sDCM) and were compared using Bayesian Model Selection (BMS) for group studies.
Group fixed-effects results indicated that bilateral IPL and ITG exhibited high neural activity at a corrected significant
level (pFWE < 0.05). Neural activity was centered in ITG (-32/2/-38) in the left hemisphere but shifted to IPL (32/-38/50) in
the right hemisphere indicating different control center for both hemispheres. BMS selected bilinear model as the optimal
model for both hemispheres (model posterior probability ~ 1.0; log evidence > 1000) which has the best balance between
model accuracy and difficulty. The minimum free energy (F) = -4.41 × 104
and -4.09 × 104
for left and right hemisphere
bilinear models respectively. From BMS and DCM results, it was found that IPL and ITG do have a dynamic collaboration
between each other, a connectivity that belongs to a greater network when the brain is at rest. The intrinsic connections
between them are negative in both directions i.e. IPL and ITG mutually inhibited each other. The effective connectivity
was modulated by the endogenous fluctuation of the brain signal.
Proses penuaan seringkali dikaitkan dengan kemerosotan pada sistem kognitif. Kemerosotan kognitif bermula seawal
usia dua puluhan dan berterusan secara linear. Selain itu, kemerosotan kognitif juga menjadi lebih nyata dengan
kehadiran hingar latar. Walau bagaimanapun, kesan penuaan ke atas mekanisme pemprosesan persepsi pertuturan
menggunakan tugasan mengulang secara terus (FRT) dalam senyap dan hingar belum difahami dengan jelas. Dalam
kajian ini, pengimejan resonans magnet kefungsian (fMRI) digunakan untuk membandingkan kesan penuaan ke atas
kehubungan efektif otak yang terhasil daripada tugasan FRT ke atas subjek normal dengan empat kumpulan umur yang
berlainan iaitu 20 - 29 tahun (n = 15), 30 - 39 tahun (n = 15), 40 - 49 tahun (n = 10) dan 50 - 65 tahun (n = 14). Satu siri
lima perkataan yang diselang-seli dalam keadaan hingar dengan senyap diberikan secara auditori. Pemetaan statistik
berparameter (SPM8) dan pemodelan dinamik penyebab (DCM10) digunakan untuk menentukan kehubungan efektif otak.
Kawasan yang terlibat dalam pembinaan model kehubungan efektif otak adalah STG, HG dan PCG. Model optimum yang
dipilih dalam kajian ini adalah model yang menunjukkan keseimbangan antara ketepatan dan kesukaran. Keputusan
fMRI kehubungan efektif menunjukkan bahawa komunikasi antara intrahemisfera tidak berubah dengan menggunakan
tugasan FRT ini apabila seseorang semakin berusia, tetapi komunikasi antara interhemisfera menjadi semakin kompleks.
Objective: A baseline functional magnetic resonance imaging (fMRI) study was carried out on a healthy right-handed male subject to attain further insights into the basic neuronal control mechanisms of bimanual and unimanual movements of hand fingers, an area that is still not fully understood. Methods : The study used the basic unimanual and bimanual movements of the left- and right-hand fingers to stimulate neuronal activity in the cerebral cortices. The subject was instructed to sequentially press his fingers either unimanually (UNI) or bimanually (BIM), against the thumb in a consistent alternative manner during the functional scans. The data were analysed using the MATLAB and SPM2 software packages. Results : Brain activations obtained via the F-test indicate a larger activation area as compared to that obtained from the T-test. The results showed that, the activated brain regions due to the self-paced finger movements are the precentral and postcentral gyrii covering the primary motor, premotor and somatosensory primer areas. The activestate signal intensity was found to be significantly (p < 0.05) higher than that of the resting-state. For UNI, brain activation showed contra-laterality with a larger activation area and a higher signal intensity at the point of maximum intensity for the left-hand finger
movement (UNIleft) compared to the right-hand finger movement (UNIright). Small ipsilateral activations were observed during UNIright and UNIleft. For BIM, the activation was observed in both hemispheres with the right hemisphere showing a higher signal intensity and coverage. The results support the fact that for a right-handed person performing either UNI or BIM type of movement, the activated motor area on the right hemisphere of the brain (movement of the left hand fingers) experience a higher intensity and larger coverage of hemodynamic response compared to the left hemisphere of the brain (movement of the right hand fingers). Analyses performed on the activated regions of interest (ROI) by
comparing the unimanual and bimanual types of activations revealed that during BIM, there are voxels in the left hemisphere controlling the movement of the left hand fingers (BIMleft) and voxels in the right hemisphere controlling the movement of the right hand fingers (BIMright). The interactions observed in this study resemble the existence of interhemispheric connection between both hemispheres during BIM. Conclusion : Although this is a single subject study, the hemodynamic response and the neuronal control mechanism in the cerebral cortices based on the BOLD mechanism can be studied and evaluated using fMRI and SPM.
This study investigated the functional specialisation characteristics of brain in multiple right-hand dominant subjects pertaining to the activation of the cerebral motor cortices evoked by unilateral finger tapping, especially in primary motor (M1) and supplementary motor (SMA) areas. This multiple-subject study used unilateral (UNIright and UNIleft) selfpaced tapping of hand fingers to activate the M1 and SMA. Brain activation characteristics were analysed using statistical parametric mapping (SPM). Activation for UNIright and UNIleft showed the involvement of contralateral and ipsilateral M1 and SMA. A larger activation area but with a lower percentage of signal change (PSC) were observed in the left M1 due to the control on UNIright (4164 voxels at a = 0.001, PSC = 1.650) as compared to the right M1 due to the control on UNIleft (2012 voxels at a = 0.001, PSC = 2.377). This is due to the influence of the tapping rate effects which is greater than what could be produced by the average effects of the dominant and sub-dominant hands. The significantly higher PSC value observed in the right M1 (p < 0.05) is due to a higher control demand used by the brain in coordinating the tapping of the sub-dominant fingers. The findings obtained from this study showed strong evidence of the existence of brain functional specialisation and could be used as baseline references in determining the most probable motor pathways in a sample of subjects.
Objective: This study investigates functional specialisation in, and effective connectivity between the
precentral gyrus (PCG) and supplementary motor area (SMA) in seven right handed female subjects.
Methods: Unimanual (UNIright and UNIleft) and bimanual (BIM) self-paced tapping of hand fingers were
performed by the subjects to activate PCG and SMA. Brain activations and effective connectivity were
analysed using statistical parametric mapping (SPM), dynamic causal modeling (DCM) and Bayesian
model selection (BMS) and were reported based on group fixed (FFX) and random (RFX) effects
analyses. Results: Group results showed that the observed brain activation for UNIright and UNIleft fulfill contralateral behavior of motor coordination with a larger activation area for UNIright. The activation for BIM occurs in both hemispheres with BIMright showing higher extent of activation as compared to BIMleft. Region of interest (ROI) analyses reveal that the number of activated voxel (NOV) and percentage of signal change (PSC) on average is higher in PCG than SMA for all tapping conditions. However, comparing between hemispheres for both UNI and BIM, higher PSC is observed in the right PCG and the left SMA. DCM and BMS results indicate that most subjects prefer PCG as the intrinsic input for UNIright and UNIleft. The input was later found to be bi-directionally connected to SMA for UNIright. The bi-directional model was then used for BIM in the left and right hemispheres. The model was in favour of six out of seven subjects. DCM results for BIM indicate the existence of interhemispheric connectivity between the right and left hemisphere PCG. Conclusion: The findings strongly support the existence of functional specialisation and integration i.e. effective connectivity in human brain during finger tapping and can be used as baselines in determining the probable motor coordination pathways and their connection strength in a population of subjects.
Kajian ke atas sifat kehubungan efektif dalam korteks auditori dilakukan ke atas lima orang subjek Melayu lelaki sihat berumur antara 20 hingga 40 tahun menggunakan pengimejan resonans magnet kefungsian (fMRI), pemetaan statistik berparameter (SPM5) dan pemodelan dinamik penyebab (DCM). Paradigma pengimejan senyap digunakan untuk mengurangkan artifak bunyi pengimbas di atas imej kefungsian. Subjek dikehendaki menumpukan perhatian kepada stimulus hingar putih yang diperdengarkan secara binaural pada keamatan 70 dB lebih tinggi daripada aras pendengaran manusia normal. Pengkhususan kefungsian dikaji menggunakan perisian SPM5 yang berasaskan Matlab melalui analisis kesan malar (FFX), kesan rawak (RFX) dan konjunksi. Analisis individu ke atas semua subjek menunjukkan pengaktifan bilateral yang tidak simetri di antara korteks auditori kanan dan kiri pada kawasan Brodmann (BA)22, 41 dan 42 melibatkan korteks auditori primer dan sekunder. Tiga kawasan auditori di korteks auditori kanan dan kiri tersebut dipilih untuk penentuan kehubungan efektif melalui pembentukan sembilan model rangkaian. Kehubungan efektif ditentukan ke atas empat daripada lima subjek dengan mengecualikan seorang subjek yang mempunyai koordinat BA22 yang terletak terlalu jauh daripada koordinat BA22 yang diperoleh daripada analisis kumpulan. Keputusan DCM menunjukkan kewujudan kehubungan efektif di antara ketiga-tiga kawasan auditori yang dipilih di kedua-dua korteks auditori. Pada korteks auditori kanan, BA42 dikenalpasti sebagai pusat masukan dengan kehubungan efektif satu arah selari BA42 → BA41 dan BA42 → BA22. Walau bagaimanapun, untuk korteks auditori kiri, pusat masukan adalah BA41 dengan kehubungan efektif satu arah selari BA41→BA42 dan BA41→BA22. Kehubungan di antara kawasan auditori yang mengalami pengaktifan mencadangkan kewujudan lintasan isyarat dalam korteks auditori walaupun semasa subjek mendengar bunyi hingar.
In this study, the asymmetry of the main effects of action, background and tonal frequency during a pitch memory processing
were investigated by means of brain activation. Eighteen participants (mean age 27.6 years) were presented with low and
high frequency tones in quiet and in noise. They listen, discriminate and recognize the target tone against the final tone
in a series of four distracting tones. The main effects were studied using the analysis of variance (ANOVA) with action (to
wring (rubber bulb) vs. not to wring), background (in quiet vs. in noise) and frequency (low vs. high) as the factors (and
levels respectively). The main effect of action is in the right pre-central gyrus (PCG), in conformation with its contralateral
behavior. The main effect of background indicated the bilateral primary auditory cortices (PAC) and is right lateralized,
attributable to white noise. The main effect of frequency is also observed in PAC but bilaterally equal and attributable to
low frequency tones. Despite the argument that the temporo-spectral lateralization dichotomy is not especially rigid as
revealed by the main effect of frequency, right lateralization of PAC for the respective main effect of background clearly
demonstrates its functional asymmetry suggesting different perceptual functionality of the right and left PAC.
High sensitivity signal detection for a sparse temporal sampling (STS) functional magnetic resonance imaging (fMRI) is compensated by the increase in the number of scans (Ns) and consequently the scan time. A long scan time would result in fatigue and restlessness in participants, while a short scan time is undesirable for an STS-fMRI due to insufficient Ns for averaging. The purpose of this study was to determine the Ns practically sufficient for a sparse fMRI study. Eighteen participants were presented with white noise during a sparse fMRI scan. The height extent of activation was determined via t statistics and region of interest (ROI) based percentage of signal change (PSC). The t statistics and PSC for Heschl’s gyrus (HG) and superior temporal gyrus (STG) during which the participants listened to the white noise were calculated for different number of scans which were 6, 12, 18, 24, 30 and 36. The t statistics and PSC values calculated for the bilateral HG and STG qualitatively indicated a minimal change over Ns = 12 to 36. Both ROIs showed a consistent common right lateralization of activation for all Ns, indicating the right-hemispheric dominance of auditory cortex in processing white noise stimulus. It was proposed that for a sparse fMRI study, Ns may practically fall between 12 and 36