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At least 703 records · Page 39Linked to original sources
PubMed1993

Estimating regional brain activity from evoked potential fields on the scalp.

Potential fields on the surface of the brain were estimated from discretely sampled scalp fields in human subjects. Relatively simple methods of linear algebra were combined with detailed anatomical information from magnetic resonance imaging. The method was verified using a tank model of the human head that encased a fully hydrated human skull in a polymer matrix of controlled resistivity matching that of human brain and scalp. Brain surface fields evoked by checkerboard contrast reversal, spread less than their scalp field counterparts, and provided information helpful in localizing brain activity.

Brain↗
PubMed1995

Correlation between skull thickness asymmetry and scalp potential estimated by a numerical model of the head.

The contribution of asymmetric skull thickness to the scalp potential amplitude was investigated numerically. The model consisted of four conductive layers representing the scalp, the skull, the cerebrospinal fluid, and the cortex with a current dipole in the occipital region. The potential created by the dipole was calculated assuming quasistatic formulation and linear media. The governing equation was discretized by the finite volume method to ensure the conservation of fluxes even in regions with abrupt changes of the conductivity. The large set of the algebraic equations for the electric potential was solved iteratively by the successive overrelaxation method. The model confirmed previous experimental studies suggesting that the potential amplitude is 60% smaller on the side with the thicker bone if the asymmetry of the skull thickness exceeds 40%. The model developed suggests that skull thickness asymmetry can create nonnegligible asymmetries in the potential measured on the scalp above homotopic points of the two hemispheres.

Adult↗
PubMed1996

A modified boundary element method for the estimation of potential fields on the scalp.

A modified boundary element method (BEM) for the calculation of potential fields on the scalp is proposed and tested in a three-shell model. The method greatly reduces the computational burden with only a small cost in accuracy. The resistivity of the skull is taken as infinite and the potential field on the inner skull surface is calculated using the standard BEM method for a one-surface system. Then the potential at any single selected point on the scalp is calculated directly from Green's theorem. The method does not give an accurate estimate of the magnitude of the potential on the scalp, but it does preserve correct relative magnitudes over all source locations in the head.

Electroencephalography↗
PubMed1999

Estimating cortical potentials from scalp EEG's in a realistically shaped inhomogeneous head model by means of the boundary element method.

Cortical potentials are estimated from scalp potentials using a realistically shaped inhomogeneous head model, by means of the boundary element method (BEM). A new adaptive algorithm has been developed to achieve high accuracy to link directly the cortical potentials to the scalp potentials in a realistically shaped inhomogeneous head model including the thin low-conductivity skull layer. Computer simulations using a concentric three-spheres head model have tested this approach. The present study demonstrates that the cortical potentials can be directly estimated from the scalp potentials using the BEM in a realistically shaped inhomogeneous head model.

Algorithms↗
PubMed1984

Minoxidil stimulates cutaneous blood flow in human balding scalps: pharmacodynamics measured by laser Doppler velocimetry and photopulse plethysmography.

In a double-blind study with randomly assigned topical solutions of 0%, 1%, 3%, or 5% minoxidil, the blood flow in balding scalps of 16 human volunteers was measured by the noninvasive techniques of both laser Doppler velocimetry (LDV) and photopulse plethysmography (PPG). On two consecutive days, an 0.25-ml volume of the assigned minoxidil formulation was spread uniformly over a 100-cm2 area of each side of the bald scalp and cutaneous blood flow was recorded for the following 4 h. Both measurement techniques showed that the 5% minoxidil solution stimulated the microcirculation of the bald scalp. Increased blood flow was greater with the 5% minoxidil solution than with the other treatments. Measured by LDV on day 1, the increase (p less than 0.0001) in blood flow occurred within 15 min of application of the 5% solution of minoxidil and was maintained at least through hour 1. On day 2, LDV showed blood flow stimulation with the 5% solution was 3-fold (p less than 0.0001) within 15 min of application and was so maintained for about 1 h. Measured by PPG, the only statistically significant (p less than 0.01) response occurred with the day 2 application of the 5% minoxidil solution. PPG is dependent on local blood volume and is only weakly correlated to cutaneous blood flow, which makes it unsuitable for this kind of study. Analysis of vital signs for days 1 and 2 revealed no systemic effect from treatment with minoxidil, suggesting that the blood flow stimulation was directly related to the topical application of minoxidil.

Administration, Topical↗
PubMed1986

Quantification of scalp hair--a computer-aided methodology.

A method for obtaining a quantitative assessment of hair density is described. First, a photographic image of the scalp is digitized onto a high-resolution computer graphics screen. Second, the frequency of each of 256 gray levels (one for each of 500 vertical X 500 horizontal = 250,000 locations on the screen) is obtained and the frequency histogram of gray levels is displayed. Third, a statistical procedure, gaussian mixture analysis, is used to resolve the frequency distribution into two normally distributed component distributions. The first component distribution describes the range of gray levels that are typically associated with hair. The second component distribution describes shades of gray that are typically associated with scalp. The statistical model provides a precise measure of the proportion of the head that exhibits gray levels in each of the two component distributions (hair or scalp). The proportion of the first component distribution is a scale-independent measure of hair density. The difference in this quantity before and after treatment provides an accurate quantitative determination of the change in hair density and hence of the efficacy of treatment.

Alopecia Areata↗
PubMed1994

Immunocytochemical localization of androgen receptors in the scalp of the stumptail macaque monkey, a model of androgenetic alopecia.

The purpose of this study was to identify the distribution of androgen receptors in the bald and hairy scalp of adult male and female stumptail macaque monkeys by light microscopic biotin-avidin immunocytochemistry with a highly purified rat monoclonal antibody against the cloned human androgen receptor. Consistent, intense nuclear and minimal cytoplasmic immunostaining was observed in several distinct cell populations of the pilosebaceous unit including the dermal papilla, hair epithelium, outer root sheath, dermal sheath, and sebaceous gland. A similar distribution of androgen receptors was found in miniaturized and terminal anagen and telogen follicles of the bald and hairy scalp, respectively. Binding of androgen receptor antibody was also detected in dermal fibroblasts, basal and intermediate layers of the interfollicular epidermis, and duct and glandular cells of eccrine sweat glands. This investigation demonstrates the presence of androgen receptors in the pilosebaceous unit of the scalp of the stumptail macaque and also shows that their distribution is comparable to that previously reported for humans.

Alopecia↗
PubMed1991

Effect of androgens on the growth of cultured human dermal papilla cells derived from beard and scalp hair follicles.

Androgens stimulate hair growth in some areas, e.g., beard, but may cause regression and baldness on the scalp. The mesenchyme-derived dermal papilla is believed to regulate many aspects of hair growth. It is probable that androgens exert their effect on hair growth via the dermal papilla. In this study the effect of androgens on the growth of cultured dermal papilla cells from beard and non-balding scalp was assessed. Dermal papilla cells from beard hair follicles and non-balding scalp were cultured in vitro in the presence and absence of different concentrations of testosterone or the synthetic, non-metabolizable androgen, mibolerone. Cell growth was reflected by the incorporation of 3H-thymidine. The presence of either androgen did not significantly alter DNA synthesis at any of the concentrations examined in either type of cell line. These results do not mean that dermal papilla cells do not respond to androgens in vitro, but that the measurement of cell growth is an inappropriate method of assessment. Androgens may well stimulate the synthesis of specific proteins that could influence the hair follicle.

Androgens↗
PubMed2006

Female patients complaining about hair loss: documentation of defective scalp hair dynamics with contrast-enhanced phototrichogram.

BACKGROUND: The complaint of chronic hair loss frequently affects female subjects and there is little or no objective technology available in the general dermatology or even in the hair clinics to guide the observer in the management of the patient. The purpose of this report is to share the results of refined hair growth measurements that were collected in 92 female subjects complaining about hair loss. METHODS: Clinically they were classified as having a patterned hair loss according to Ludwig (L; n=50), diffuse hair loss (D; n=13) or no visible hair loss but complaining of hair shedding (N; n=29). Two scalp sites on the top of the head and one occipital site were investigated after clipping by close-up photography before and after a hair dye (contrast enhancement, CE). Forty-eight hours later a new photograph was taken after CE in view of phototrichogram analysis (CE-PTG). Finally a last hair clip was performed 30 days later and hair thickness and length determined for linear growth measurements (LHGR). RESULTS: Herein we confirm that the top of the head shows usually a higher hair density than occipital sites, a physiological observation that applies both to men and women. From the technological perspective, we also document that CE improves hair detection in all sites. Interestingly, in affected patients (L and D) the relative increase of hair counts after CE was much higher (range +22.4% to +28.3%) compared with apparently unaffected females (N; range +8.2% to +9.7%). This increase in hair counts was only due in part to the presence of less pigmented thinning hair (thickness less than 40 microm). Such thin hairs were found in statistically significantly higher proportions in younger patients with mildly severe (grade I) patterned alopecia (Ludwig: L). In other patients with hair loss and in more severe forms of patterned alopecia - especially in older patients - the thin hair is not detected in abnormal proportions. In all sites slower growth rates and decreased anagen percentages indicate a defective hair replacement programme distinguishing L patterns from diffuse hair loss and from apparently unaffected patients complaining of chronic hair loss. Globally, we also noted that increasing age is associated with significant regression of scalp hair (decreased hair counts, thinner hair and slower LHGR). CONCLUSION: On the basis of the present data together with female data from the literature and our own studies in male subjects, we suggest a three-step mechanism leading to hair loss 1. Shortening of growth phase the hair cycle with maintained thick hair, i.e. more frequent hair cycling that leads to more hair shedding. 2. Intermittent production of short thin hair, i.e. morphological evidence of miniaturisation. 3. Very occasional or almost no hair production, i.e. dormant follicles or irreversible follicular atrophy. Depending on the genetic background, hormonal microenvironment in the scalp and conditioning of individual hair follicle bio-responses, female and male patterned hair loss may end up into different phenotypes.

Alopecia↗
PubMed2005

Dermocosmetic aspects of hair and scalp.

Hair cosmetic agents are preparations intended for placing in contact with the hair and scalp, with the purpose of cleansing, promoting attractiveness, altering appearance, and/or protecting them in order to maintain them in good condition. Current shampoo formulations and styling products are tailored to the variations associated with age, gender, hair quality, hair care habit, and specific problems relating to the superficial condition of the scalp. The great amount of variables to be accounted for, some of them contradictory and hard to bring into accord, makes adequate product formulation a challenge and requires continuous research. Recent hair cosmetic developments include topical hair growth stimulants, photoprotectors, and anti-aging compounds. The advances in molecular technology have opened the avenue to the study of the molecular basis of hair growth and its deviations, as well as of the aging process. The discovery of potential pharmacological targets and the development of selective and effective delivery systems following topical application indicate further strategies for maintenance of healthy hair and scalp in the young and old.

Hair Diseases↗
PubMed1989

Eczema of the face, scalp and neck: an epidemiological comparison by site.

Fifteen percent of 3684 patients with eczema attending a contact clinic presented with head and/or neck eczema. There were epidemiological differences among eczema rashes occurring on different parts of the head and neck. Of the 538 patients with head and/or neck eczema, 345 (64%) occurred solely on the face, 52 (10%) on the eyelids, 49 (9%) on the lips, 20 (4%) on the ears, 22 (4%) on the scalp, and 21 (4%) on the neck. Twenty-nine (5%) had eczema on more than one area of the head/neck. The mean age was lowest in patients with lip eczema (27.5 years) and highest in patients with eyelid eczema (37 years) (p = 0.0056). The proportion of females with eczema was higher than males in all groups except the scalp eczema group. Contact dermatitis was more prevalent in the ear eczema (80%) and neck eczema (76%) groups, while endogenous/unclassifiable eczema was more prevalent in the lip eczema (72%) and scalp eczema (73%) groups (p less than 0.0001). Allergic contact dermatitis was more common than irritant contact dermatitis.

Adolescent↗
PubMed2001

Contact leukoderma of the scalp or an unusual variant of vitiligo?

Contact leukoderma due to hair dyes is strongly suspected in patients presenting with depigmented patches sharply localized to the scalp. We describe three patients with a striking pattern of depigmentation, which stopped abruptly at the hair margins. However, no definite correlation with the use of hair dyes could be made in any of them. Our cases represent an unusual pattern of vitiligo of the scalp, which seems to have been previously attributed mainly to hair colorants. Careful examination of the lesions on the scalp may reveal more cases with this pattern.

Adolescent↗
PubMed1980

Lichen sclerosus et atrophicus of the scalp.

A patient is described who developed pruritic lesions of the scalp with increasing hair loss and plaque formation over a period of 15 years, in association with patches of white atrophic skin on her trunk and vulva in the last 5 years. Biopsies of the scalp and trunk lesions both showed lichen sclerosus et atrophicus. This would appear to be the first recorded case of lichen sclerosus et atrophicus of the scalp in the English literature.

Aged↗
PubMed1983

A more reliable photometric technique for the measurement of scalp sebum excretion.

The objective assessment of antiseborrhoeic therapy for the scalp requires a reliable technique for the measurement of sebaceous gland activity. Previously published methods were tried but found to be unreliable. This paper describes a photometric technique which gave repeatable results and demonstrated a reduction of sebaceous gland activity on the scalp with both oral isotretinoin and topical II alpha-hydroxyprogesterone. The accuracy of the method was achieved by careful preparation of the scalp but was affected by recent shampooing.

Adult↗
PubMed1987

Treatment of seborrhoeic dermatitis with ketoconazole: I. Response of seborrhoeic dermatitis of the scalp to topical ketoconazole.

A randomized, double-blind, placebo-controlled cross-over study was made of ketoconazole shampoo in the treatment of 20 subjects with seborrhoeic dermatitis of the scalp. Responses were measured by clinicians using clinical gradings, and by the patients using a linear analogue scale. Scaling and itching of the scalp improved significantly with ketoconazole and no response was seen with placebo. Topical ketoconazole appears to be an effective therapy for seborrhoeic dermatitis of the scalp, and more suitable for long-term treatment than the oral preparation.

Administration, Topical↗
PubMed1992

Failure of passive transfer of serum from patients with alopecia areata and alopecia universalis to inhibit hair growth in transplants of human scalp skin grafted on to nude mice.

We have previously demonstrated regrowth of hair in scalp skin grafts taken from patients with alopecia areata (AA) and alopecia universalis (AU) following engraftment on to nude mice. This present study was to determine whether serum from patients with AA and AU, has a role in the process of hair loss and the role of antibodies and complement. Forty mice were grafted with transplants obtained from seven patients. One group of the grafted mice was given patients' serum and another group normal serum. The mice were treated topically with cyclosporin (CyA), or olive oil. Hair growth was noted in most grafts and intravenous injections of serum did not prevent or inhibit this process. Immunofluorescence studies before grafting showed deposition of immunoglobulins and complement in hair follicles in both normal and affected scalp skin, but a more striking deposition was noted in the affected skin. Deposition of immunoreactants after grafting was observed only after the injection of serum from the patients but not with normal serum. Thus the sera from patients with AA or AU, when injected into nude mice with hair transplants from the scalp skin of patients with these disorders, does not alter the hair growth despite deposition of immunoreactants around the hair follicles.

Alopecia↗
PubMed1992

Bullous and haemorrhagic lichen sclerosus with scalp involvement.

We describe a patient who developed a generalized blistering eruption due to lichen sclerosus and who was observed to have scalp involvement. Both are unusual manifestations of this disease which merit consideration. Lichen sclerosus is an uncommon disease that most frequently affects the external genitalia of perimenopausal women. The aetiology is unknown. Approximately 20% of affected patients have extragenital lesions that present as small, ivory, shiny round macules or papules that later become atrophic; extragenital lesions are generally asymptomatic. Bullous and haemorrhagic forms may occur but these are generally localized and reports of extensive or generalized involvement are rare. We describe an elderly woman with generalized bullous lichen sclerosus. As an incidental finding, she was observed to have lichen sclerosus affecting her scalp. This has rarely been described and it would appear that she is the third reported case of scalp involvement.

Aged↗
PubMed1993

Differences in testosterone metabolism by beard and scalp hair follicle dermal papilla cells.

OBJECTIVE: Androgens have paradoxically different effects on hair follicles depending on body site, stimulating beard growth while inducing regression in some areas of the scalp. The mesenchyme derived dermal papilla at the base of the hair follicle regulates many aspects of the growth of follicular epithelium, and is probably the site of androgen action. Since 5 alpha-dihydrotestosterone is considered to be the active intracellular androgen in many target tissues and is required for some androgen-mediated hair growth, such androgen-sensitive cells should contain 5 alpha-reductase. This study was designed to investigate whether cultured human dermal papilla cells contain 5 alpha-reductase and whether the metabolic capacity varies with the body site of the follicle in line with the clinical picture. DESIGN: Testosterone metabolism in cultured dermal papilla cells from androgen sensitive beard follicles was compared with less androgen dependent non-balding scalp follicles. Primary cell cultures were established from follicles of 11 patients with normal hair growth. The cells were grown to confluence in 10-cm Petri dishes and incubated with 5 nM 3H-testosterone in serum-free medium for 2 hours. The cells and the culture medium were collected separately for individual analysis. MEASUREMENTS: Unlabelled carrier and 14C-marker steroids were added to both the cell and medium extracts before separation by thin-layer chromatography. The individual steroid identities were confirmed by recrystallizing up to five times to a constant 3H/14C ratio. RESULTS: Testosterone was taken up by both cell types; significant amounts of 5 alpha-dihydrotestosterone were recovered inside beard cells, but not in scalp cells, whereas androstenedione was identified in both. An unidentified compound was present intracellularly in both cell types, but was not present in the culture medium. 5 alpha-Dihydrotestosterone was present only in the culture medium of beard cells but androstenedione was present in a similar amount in the medium from both cell types. The presence of other steroids could not be confirmed in either the cell extracts or the culture medium. CONCLUSIONS: The production of 5 alpha-dihydrotestosterone by beard cells concurs with the poor beard growth in men with 5 alpha-reductase deficiency, supporting our hypothesis that androgens mediate their effects on the hair follicle via the mesenchyme-derived dermal papilla.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗