Design and use of novel non-invasive head immobilisation method for investigation of behavioural and functional asymmetries in non-human primate auditory cortex

Abstract

This project was initiated with two goals in mind. The first, to refine methods of head immobilisation for rhesus macaques participating in experiments which do not require direct access to the brain, and the second to investigate the effect of attention on lateralisation in auditory cortex. Head immobilisation is often necessary for neuroscientific procedures. A number of Non-invasive Head Immobilisation Systems (NHIS) for monkeys are available, but the need remains for a feasible integrated system combining a broad range of essential features. This thesis details the development of an individually customised macaque NHIS which addresses several animal welfare and scientific needs. The system comprises a customised facemask that can be used separately or combined with a back piece to form a full head helmet. The system was evaluated during performance on several auditory or visual behavioural tasks with testing sessions lasting 1.5-2hrs. To investigate the effect of attention on lateralised processes, four male rhesus macaques were trained to perform an active auditory spatial discrimination task (two of which used the NHIS) using either conspecific “coo” vocalisations or a coo vocalisation from a different individual which had the phase information scrambled, but preserved the spectral components (sCoo). Behavioural results indicated a directional bias during the task with coos, with the animals performing the task with ease when the coo initially appeared on the left but performance being hindered when the coo first appeared on the right. No bias was observed with an animal initially trained with the noise. Attention effects on hemispheric laterality were then studied using fMRI with the trained animals and, as a point of reference, a naïve animal who was passively presented with the task stimuli. The results shown have implications for the control of attention when investigating lateralised processing in both human and non-human species. Additionally, it is conclusively shown that auditory fMRI and behavioural experiments can be conducted without the need for invasive head immobilisation techniques in rhesus macaques.