Recovery after chronic stress within spatial reference and working memory domains: correspondence with hippocampal morphology.

Chronic stress results in reversible spatial learning impairments in the Morris water maze that correspond with hippocampal CA3 dendritic retraction in male rats. Whether chronic stress impacts different types of memory domains, and whether these can similarly recover, is unknown. This study assessed the effects of chronic stress with and without a post-stress delay to evaluate learning and memory deficits within two memory domains, reference and working memory, in the radial arm water maze (RAWM). Three groups of 5-month-old male Sprague-Dawley rats were either not stressed [control (CON)], or restrained (6 h/day for 21 days) and then tested on the RAWM either on the next day [stress immediate (STR-IMM)] or following a 21-day delay [stress delay (STR-DEL)]. Although the groups learned the RAWM task similarly, groups differed in their 24-h retention trial assessment. Specifically, the STR-IMM group made more errors within both the spatial reference and working memory domains, and these deficits corresponded with a reduction in apical branch points and length of hippocampal CA3 dendrites. In contrast, the STR-DEL group showed significantly fewer errors in both the reference and working memory domains than the STR-IMM group. Moreover, the STR-DEL group showed better RAWM performance in the reference memory domain than did the CON group, and this corresponded with restored CA3 dendritic complexity, revealing long-term enhancing actions of chronic stress. These results indicate that chronic stress-induced spatial working and reference memory impairments, and CA3 dendritic retraction, are reversible, with chronic stress having lasting effects that can benefit spatial reference memory, but with these lasting beneficial effects being independent of CA3 dendritic complexity.

Effects of exercise training on hearing ability.

This study was designed to determine whether improvements in both cardiovascular fitness and hearing sensitivity occurred following 2 months of aerobic exercise training. Seventeen moderately-low fit (VO2 peak <32 ml/kg/min) young adults were evaluated for cardiovascular fitness and pure-tone and temporary threshold shifts (TTS) at 2, 3, and 4 kHz before and following 10 min of noise. Subjects exercised for 8 weeks by cycling on a bicycle ergometer at 70% of their peak oxygen consumption (VO2 peak). Average VO2 peak increased 34% (p < 0.05) above pre-exercise training levels. Both pure-tone hearing (2 and 3 kHz) and TTS improved following 2 months of exercise training at the evaluated frequencies (2, 3, and 4 kHz) (p < 0.05). Cardiovascular health as indicated by VO2 peak was associated with hearing sensitivity. Although the mechanisms have not been identified, these results support the existence of a cardiovascular health-hearing synergism.

The efficacy of utilizing the P300 as a measure of auditory deprivation in monaurally aided profoundly hearing-impaired children.

Auditory event-related responses have been successfully used to differentiate the effects of auditory deprivation in laboratory animals and could provide an alternative and less subjective method of testing auditory deprivation. The purpose of this study was to investigate the efficacy of using the P300 response to measure auditory deprivation in monaurally aided children with hearing impairment. Seventeen children (8 female, 9 male) aged 9 to 18 years (M = 13.1 years) participated in the study. Ten subjects with bilateral congenital severe to profound sensorineural hearing losses (M = 87 dB) were recruited from a residential school for the deaf. All had worn monaural amplification for at least 8 years. Seven children with normal hearing sensitivity were matched for age effects. A two-tone auditory oddball paradigm was utilized to elicit the P300 responses. Statistical analysis revealed that the P300 amplitude was significantly greater in the aided ear compared to the unaided ear of the hearing-impaired group (p < 0.05). Two unaided ears of this group had no measurable responses. No other significant latency or amplitude differences were found within or between groups. Results of this investigation serve to reconfirm that binaural amplification should routinely be recommended for hearing-impaired children.

Does cardiovascular health mediate hearing ability?

Exercise and noise exposure causes temporary hearing loss. Yet, a direct relationship may exist between cardiovascular health and hearing. The purpose of this study was to determine whether noise and exercise caused different levels of hearing loss depending on one's cardiovascular fitness. Twenty-eight volunteers were considered: high fit VO2peak = 48.5 +/- 1.6 ml.kg-1.min-1, N = 10), moderately fit VO2peak = 38.1 +/- 0.9 ml.kg-1.min-1, N = 9), and low fit VO2peak = 30.4 +/- 0.9 ml.kg-1.min-1, N = 9). Hearing ability at 2000, 3000, and 4000 Hz was assessed following 10 min of noise (N), exercise (E), and noise-and-exercise (N&E). The high fit group consistently demonstrated better hearing after all conditions compared to the low fit group. Significant differences between the high and low fit groups always occurred during N&E and sometimes during N. E did not cause significant hearing loss in any group. Cardiovascular health as indicated by a mean VO2peak = 48.5 ml.kg-1.min-1 is associated with less hearing loss after 10 min of either N or N&E. Although the mechanisms have not been identified, these results support the existence of a cardiovascular health-hearing synergism.

Cardiovascular adjustments to high- and low-intensity exercise do not regulate temporary threshold shifts.

Sixteen adults cycled for 10 min at low and high intensities--with and without noise. The noise consisted of a 1/3 octave band-filtered noise with a 2,000 Hz center frequency at 104 dB SPL. Regardless of whether or not noise was present, systolic blood pressure increased 14% and 40% above rest during low- and high-intensity exercise, respectively. Heart rate also increased above rest (36% and 90%) during low- and high-intensity exercise, respectively. Temporary threshold shifts (TTS) at 3,000, 4,000 and 6,000 Hz could not be differentiated following low- and high-intensity exercise when noise was not present. We report significant TTS at the three frequencies following 10 min of noise exposure with or without low- or high-intensity exercise. TTS was not influenced by either the 14-40% increase in blood pressure or the 36-90% increase in heart rate induced by exercise. The inability of noise alone to influence either blood pressure or heart rate appears to implicate systems other than the cardiovascular in the regulation of hearing sensitivity.

Effects of submaximal exercise and noise exposure on hearing loss.

A recent Scandinavian study reported that persons cycling at moderate intensity for 10 min suffered hearing loss when the exercise was accompanied by noise. The noise consisted of a 1/3 octave band-filtered noise with a 2000 Hz center frequency at 104 dB SPL. In the present study, adults cycled at 50 rev.min-1 against a force that elicited an oxygen cost equal to 70% of VO2max--an intensity frequently recommended in exercise prescriptions--with and without noise administered via headphones. Repeated measures ANOVA with three factors revealed that although a temporary hearing loss occurred following exercise-and-noise, a similar and slightly greater hearing loss occurred following noise-only. Hearing sensitivity was not significantly altered by exercise-only (p greater than .05). In general, hearing loss values were greatest between 3000 and 4000 Hz. In conclusion, temporary hearing loss was driven by noise exposure, not exercise. However, persons who choose to exercise with personal headphones or in a noisy environment should be aware of potential premature hearing loss.

Effects of low-intensity exercise and noise exposure on temporary threshold shift.

It is not known if an individual who is susceptible to temporary threshold shift (TTS) may also suffer permanent hearing loss. Risk for hearing loss is caused by the physical properties (frequency, intensity, and duration) of noise and other possible factors including physical exercise. Seventeen subjects cycled at 40% of maximum oxygen consumption (VO2 max) with and without noise administered via personal headphones. Exercising at 40% of VO2 max is considered to be low intensity. Hearing tests before and after these two exercise conditions and a noise-only condition indicated that TTS only occurred when noise was present, that is, exercise alone did not result in TTS. Therefore TTS and subsequent hearing loss (which only persisted for 24-48 h) was found to be driven by noise exposure, not low-intensity exercise.

Influence of sentence context on speech perception in young and older adults.

This study investigated the ability of young and older adults to use contextual cues to understand speech in ordinary listening situations. Key word recognition scores were obtained with the Speech Perception in Noise (SPIN) test. Sentence lists contained 50 key words preceded by a high predictability (HP), low predictability (LP), or a carrier phrase (CP) context accompanied by a varying background of multitalker babble. Comparison of the low context items vs the number of meaningfully rich items correctly identified provided an index of the listener's ability to use contextual information in the HP sentences. The LP and CP score reflected the individual's ability to recognize items based only on the acoustic-phonetic information of the key words. Most individuals were able to take some advantage of contextual cues in everyday sentences; however, the older listeners were more adversely affected by background noise than younger listeners. For clinical utilization of the SPIN test, further research is needed to develop normative data as a function of age to make it an "age-fair" test.

Temporal stability of psychophysiological responding: a comparative analysis of mental and physical stressors.

Although extensive research has been conducted on psychophysiological reactivity, there is a paucity of data concerning the temporal stability of such procedures. Test-retest reliability of experimental stressors from both mental and physical modalities were assessed using a wide range of psychophysiological measures. Absolute baseline and test values demonstrated adequate test-retest reliability for skin temperature, skin resistance, vasomotor response, heart rate, systolic and diastolic blood pressure, while forearm EMG had low reliability. Difference scores, which represent change from baseline to test conditions, did not have adequate reliability. These data represent a necessary step towards standardization of psychophysiological assessment techniques and thus may guide further use of more reliable methods.