Interactions between specific parameters of cannabis use and verbal memory

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Abstract

Recently, the impact of different parameters of cannabis use, including the age of first use, the average frequency of use, the cumulative lifetime dose, the average dose per occasion, and the duration of regular use upon cognitive functions has been discussed. However, to date no study has systematically investigated the interactions of these parameters with regard to cognitive performance. To determine whether these interactions exist, 142 healthy young adult cannabis users participated in a neuropsychological assessment study with a German version of the Rey Auditory Verbal Learning Test (RAVLT). In line with previous studies on cannabis use and verbal memory, significant associations between certain components of verbal memory and frequency of use, cumulative lifetime dose and duration of regular use respectively were found. Remarkably, a multivariate analysis solely revealed a significant main effect of the duration of cannabis use with regard to immediate recall and recall after interference. Moreover, the findings suggest that age of first use, duration of use and frequency of cannabis use interact with regard to their impact on different measures of verbal memory. The findings of the present study provide first evidence that particular parameters of cannabis use interact with regard to their impact on cognitive functions in unintoxicated cannabis users. This finding might deliver more insight into the complex mechanisms underlying the impaired memory functions observed in cannabis users.

Introduction

Verbal learning and memory are two of the most extensively examined impaired cognitive functions in cannabis users. A growing number of studies suggest performance deficits in acutely intoxicated subjects in terms of immediate and delayed recalls of words, intrusion and learning (D'Souza et al., 2004, Ilan et al., 2004, Curran et al., 2002). Concerning the recent debate whether these impairments persist, neuropsychological studies of heavy or long-term cannabis users in the unintoxicated state consistently demonstrated impairments on word list learning tasks. These tasks assess the ability to encode, consolidate, store and retrieve verbal episodic information and are highly sensitive to neurological impairment (Lezak et al. 2004), albeit, performance is also affected by age, general intelligence and education (Schmidt 1996). In general, all verbal learning task measures (immediate and delayed recall, acquisition learning as well as recognition) have been associated with performance deficits in cannabis users (Solowij and Battisti 2008). However, these studies differ in terms of modality and amount of memory impairments found. Solowij and Battisti (2008) bring forward the argument that specific parameters of cannabis use are developed differently in the various study samples.

In general, various specific parameters of cannabis use have been associated with cognitive impairments. Most recently, the age of first use was associated with detrimental adverse effects (Rubino and Parolaro, 2008, Schneider, 2008). For instance, early onset cannabis users exhibited poorer cognitive performance than late-onset users or control subjects, especially in verbal IQ (Pope et al. 2003). Furthermore, Brook et al. (2008) found a negative association between earlier marijuana use and later academic achievement and functioning. Early use of cannabis has also been linked to long-lasting effects on attentional functions in adulthood (Ehrenreich et al. 1999). Moreover, the ability to focus attention and filter out irrelevant information was progressively impaired with the duration of use (Solowij et al. 1995). Furthermore, the speed of information processing was significantly delayed with an increasing frequency of use (Solowij et al. 1995). Finally, high frequent use was related to impaired performance on tests assessing memory, executive functioning, psychomotor speed and manual dexterity (Indlekofer et al., 2009, Bolla et al., 2002).

With regard to verbal memory, several usage parameters have been shown to affect performance. The duration of cannabis use was associated with poorer performance on all learning trials of the Rey Auditory Verbal Learning Test (Messinis et al., 2006, Solowij et al., 2002). The frequency of cannabis use has been associated with poorer performance on almost every measure of the California Verbal Learning Test (Pope et al., 2001, Pope and Yurgelun-Todd, 1996). Moreover, the cumulative lifetime dose was linked to poorer performance on measures of verbal learning and memory (Bolla et al. 2002). Finally, increasing lifetime use of cannabis was associated with a reduced ability to recall a short passage of prose immediately and delayed (Indlekofer et al. 2009).

In spite of these findings, to the best of the authors’ knowledge, no prior study systematically examined the interactive impact of different parameters of cannabis use on cognitive functions in the unintoxicated state. We therefore aimed at clarifying the occurrence and characteristics of specific parameters of cannabis use in a large sample of cannabis users in order to analyze their impact on verbal memory. In the present study, a German version of the Rey Auditory Verbal Learning Test (RAVLT, Rey 1964) was applied to assess verbal declarative memory function. It is assumed to replicate the aforementioned findings, suggesting an association between cannabis use and components of verbal memory. Furthermore, we hypothesized that different parameters of cannabis use interact with regard to their impact on verbal memory performance.

Section snippets

Participants

142 cannabis users (93 males, 49 females, age range: 18–35 years, mean: 23.09 years) with no current physical and no current or previous history of neurological or psychiatric disorder (Axis I and II according to DSM-IV criteria, APA 1994) were included in the study. Further exclusion criteria comprehended intake of other illicit psychotropic substances besides cannabis on more than 5 occasions until the day of examination, a history of alcohol misuse (according to DSM-IV criteria, APA 1994) and

Characteristics and occurrence of specific parameters of cannabis use in the sample

Patterns of cannabis use and mean years of education for the whole sample are given in Table 1. After performing median splits according to the different parameters of cannabis use, each participant was assigned to either an early age (EAU, age: 11–14, mean: 13.30 years, SD = .873, N = 62) or late age (LAU, age: 15–31, mean: 16.49 years, SD = 2.143, N = 80) of first use group; to a high (HFU, 10–30 days/month, mean: 23.42, SD = 7.02, N = 74) or low (LFU, 0–9 days/month, mean: 2.73, SD = 2.88, N = 68) frequency of

Discussion

The aim of the present investigation was to examine the impact of specific parameters of cannabis use on verbal memory with a particular focus on interactions of these parameters. Therefore, occurrence and characteristics of different parameters of cannabis use including the age of first use, the frequency of use, the cumulative lifetime dose, the average dose per occasion, and the duration of regular use, were assessed in a large sample of young adult cannabis users. Thereupon, the impact of

Acknowledgments

This work was supported by a grant to E. Gouzoulis-Mayfrank and J. Daumann from the German Research Foundation (Deutsche Forschungsgemeinschaft DFG, Go 717/6-1/2).

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