, 1998). Cognitive functioning, particularly memory performance has been found to be impaired in patients with childhood onset of growth hormone deficiency and HGH replacement therapies have been found to offset this memory impairment (Arwert et al., 2005). Studies have identified a link between improved attention and increases in memory performance in children with growth hormone deficiency (Arwert et al., 2005; Arwert et al., 2006). This is due to the connection between memory capacity and attentional resources.
Growth hormone deficiency that begins in childhood is most often treated with growth hormone supplementation in order to increase body size during adolescence (Nieves-Martinez et al., 2009). Yet recent studies have demonstrated that this treatment directly correlates to improved memory in adulthood. In fact studies have suggested that treatment with growth hormone in child onset deficiencies can in fact prevent learning and memory deficits later in life (Nieves-Martinez, 2009). Childhood onset of growth hormone deficiency has been correlated to adult memory impairment. However, studies have shown that early supplementation of growth hormone in adolescence has been able to prevent age related deficiencies in learning and memory that are prominent in this population. In fact treatment of growth hormone deficiencies in adolescents was correlated with a cease in the impairment of spatial memory past adolescence (Nieves-Martinez et al., 2009). In fact, supplementing growth hormone during puberty thwarts the deterioration of brain functioning as the result of growth hormone deficiency. Adolescence is a period of maturation and HGH replacement assists the maturation of the brain which may have significant implications for the course of the illness (Nieves-Martinez, 2009).
Children who experience cognitive impairments in childhood as the result of growth hormone deficiencies are more likely to experience psychosocial problems later in life (Baum et al., 1998). Further, as adults these children have decreased employment and marriage rates. Persons who develop growth hormone deficiency as adults have been found to perceive their quality of life and overall health as poor (Baum et al., 1998). Therefore the cognitive changes of growth hormone deficiencies in adults also warrant exploration.
Growth hormone deficiency is the most common endocrine deficiency linked to pituitary disease in adults (Baum et al., 1998). During the aging process, there is a significant decrease in IGF-I protein levels in the body. There are also noticeable changes in the cerebrospinal fluid concentration of the dopamine, metabolite, and homonvanillic acids in the body (Arwert et al., 2005). Studies have shown that growth hormone replacement in adults with a deficiency has shown improvements in body composition as evidenced by an increase in bone density and lean muscle mass (Baum et al., 1998). Adults with acquired growth hormone deficiency who have undergone HGH treatments have reported improved mood, cognitive functioning, and overall sense of well being when measured on tasks of attention, memory, and perceptual motor skill (Baum et al., 1998). There has been concern that growth hormone deficiencies are correlated to learning disability and memory deficits that are commonly seen in adults who have experienced growth hormone deficiency in childhood.
As with any drug, HGH has potential negative side effects therefore one must weigh these against the potential gains associated with HGH treatment. Persons most at risk for experiencing negative side effects of HGH therapies are those that are older and out of shape. The most common side effects after HGH supplementation in adults who are growth hormone deficient include water retention, weight gain, symptoms of carpal tunnel syndrome all of which may be attributed to an increase in the sodium levels in the body (Baum et al., 1998).
However, despite these side effects, HGH treatment has been shown to improve the cognitive functions, particularly memory, in childhood onset growth deficient persons within the first year of treatment (Arwert et al., 2006). This includes improvement in short- and long-term memory tasks as well as iconic memory tasks. In adult onset growth hormone deficient patients significant improvements in memory occurred after one year with maximum benefits not being recognized until after two years of treatment (Arwert et al., 2006). In fact, after a year of treatment, memory shows significant signs of improvement and these gains could still be recognized after 10 years of treatment (Arwert et al., 2005).
The improvements in short-term memory after the first year of treatment and long-term memories after two years identify that in order to achieve increased cognitive functioning the course of treatment should be a minimum of two years in duration (Arwert et al., 2005). Individuals who experience an increase in memory function after six months may have higher IGF-I I (insulin like growth factor) levels. Persons who reported results after one year had an IGF-I level that was within normal range. At the one year mark, increases in cerebral blood flow increases as well as improvement in memory performance, including working memory. Working memory has been identified as the ability to keep information readily available should it be needed for immediate recall ad application (Arwert et al., 2005). Improved working memory can be evidenced by improved and faster memory performance as well as increased regional brain activity that can be measured with PET imaging (Arwert et al., 2005).
Researchers have found that memory processing for small memory loads is quicker in persons with higher IGH-I levels (Arwert et al., 2005). This suggests a direct link between the speed of information processing and IGF-I levels in adults. Recent studies have begun to incorporate imaging, particularly PET scans and MRI imaging, to show task-related activity in the areas of the brain associated with working memory and cognitive functioning. Images are taken to compare baseline vs. task activities and to observe changes as task load increases (Arwert et al., 2005). Arwert et al. (2005) identify that the anterior cingulated cortex is involved in response selection and error monitoring while postural parietal activity is responsible for the attentional processes and information storage. Imaging aids researchers in identifying baseline functioning in individuals so that differences in functioning between groups cannot be associated with differences in baseline. Brain activity can then be observed during task completion, while controlling for load associated activity (Arwert et al., 2005).
These studies conducted by Arwert et al. (2005) demonstrated a slower performance by the growth hormone deficient group especially as the task load began to increase. This is associated with an increase in the activity in the areas of the brain that are responsible for working memory while the growth hormone deficiency makes this task more difficult requiring increased efforts. Increased IGF-I levels were found to produce increased performance in cognitive function and working memory on tests of mental processing speed in adults. Researchers in this study found that persons with growth hormone deficiency have decreased memory speed during a working memory task. Participants were capable of normal retrieval but the task performance time was significantly slower than their non-deficient counterparts.
Additional studies have identified a distinction between long-term memory capacity in young and old rats and suggest that in addition to a decrease in the production of HGH that older persons may be less likely to respond to HGH treatment regiments due to a lack of stimulus sensitivity necessary to obtain desired results or potentially an over-reinforcement of the response (Schneider-Rivas, 1995). These studies indicated that while young rats had a positive response to growth hormone administration, that this intervention had little impact on the memory functioning of older rats (Schneider-Rivas et al., 1995). It appears that cell response to growth hormones decrease with age producing an imbalance in the body. Yet attempts at simply replacing HGH in the body have not had the significant impact that one would hope for. For example, studies have indicated that in many cases it takes years before a true change in cognitive functioning can be observed in a person undergoing HGH therapies (Arwertz et al., 2005). These studies support the concept that growth hormone levels differ between young and old persons both with and without growth hormone deficiency.
However, one must weigh the benefits of engagement in HGH replacement therapies against the length of time required to produce results. Previous reports have shown that administering HGH in older persons can provoke a reversal in certain catabolic protein indicators therefore augmenting muscle mass, improving exercise tolerance, increasing the amount of REM sleep, improved short-term and long-term memory, and resulting in an overall sense of improved well being (Schneider-Rivas et al., 1995). What remains unclear is whether it is the direct effect of the HGH treatments or another factor such as IGF-I that is provoked into action by the introduction of the growth hormone.
The decrease in growth hormone in the areas of the brain associated with memory have been shown to decrease with age and the introduction of growth hormone treatment in older adults has demonstrated an improvement in cognitive ability such as psychomotor function, memory retention, and personal care. Results have also been found in Alzheimer's patients, young adults…