Deep brain stimulation for movement disorder treatment: exploring frequency-dependent efficacy in a computational network model

A large-scale computational model of the basal ganglia network and thalamus is proposed to describe movement disorders and treatment effects of deep brain stimulation (DBS). The model of this complex network considers three areas of the basal ganglia region: the subthalamic nucleus (STN) as target area of DBS, the globus pallidus, both pars externa and pars interna (GPe-GPi), and the thalamus. Parkinsonian conditions are simulated by assuming reduced dopaminergic input and corresponding pronounced inhibitory or disinhibited projections to GPe and GPi. Macroscopic quantities are derived which correlate closely to thalamic responses and hence motor programme fidelity. It can be demonstrated that depending on different levels of striatal projections to the GPe and GPi, the dynamics of these macroscopic quantities (synchronisation index, mean synaptic activity and response efficacy) switch from normal to Parkinsonian conditions. Simulating DBS of the STN affects the dynamics of the entire network, increasing the thalamic activity to levels close to normal, while differing from both normal and Parkinsonian dynamics. Using the mentioned macroscopic quantities, the model proposes optimal DBS frequency ranges above 130 Hz.

Replay of innate vocal patterns during night sleep in suboscines

Activation of forebrain circuitry during sleep has been variably characterized as ‘pre- or replay’ and has been linked to memory consolidation. The evolutionary origins of this mechanism, however, are unknown. Sleep activation of the sensorimotor pathways of learned birdsong is a particularly useful model system because the muscles controlling the vocal organ are activated, revealing syringeal activity patterns for direct comparison with those of daytime vocal activity. Here, we show that suboscine birds, which develop their species-typical songs innately without the elaborate forebrain–thalamic circuitry of the vocal learning taxa, also engage in replay during sleep. In two tyrannid species, the characteristic syringeal activation patterns of the song could also be identified during sleep. Similar to song-learning oscines, the burst structure was more variable during sleep than daytime song production. In kiskadees ( Pitangus sulphuratus ), a second vocalization, which is part of a multi-modal display, was also replayed during sleep along with one component of the visual display. These data show unambiguously that variable ‘replay’ of stereotyped vocal motor programmes is not restricted to programmes confined within forebrain circuitry. The proposed effects on vocal motor programme maintenance are, therefore, building on a pre-existing neural mechanism that predates the evolution of learned vocal motor behaviour.

Task-dependent vocal adjustments to optimize biosonar-based information acquisition

ABSTRACTAnimals need to acquire adequate and sufficient information to guide movements, yet information acquisition and processing are costly. Animals thus face a trade-off between gathering too little and too much information and, accordingly, actively adapt sensory input through motor control. Echolocating animals provide a unique opportunity to study the dynamics of adaptive sensing in naturally behaving animals, as every change in the outgoing echolocation signal directly affects information acquisition and the perception of the dynamic acoustic scene. Here, we investigated the flexibility with which bats dynamically adapt information acquisition depending on a task. We recorded the echolocation signals of wild-caught Western barbastelle bats (Barbastella barbastellus) while they were flying through an opening, drinking on the wing, landing on a wall and capturing prey. We show that the echolocation signal sequences during target approach differed in a task-dependent manner; bats started the target approach earlier and increased the information update rate more when the task became increasingly difficult, and bats also adjusted the dynamics of call duration shortening and peak frequency shifts accordingly. These task-specific differences existed from the onset of object approach, implying that bats plan their sensory-motor programme for object approach exclusively based on information received from search call echoes. We provide insight into how echolocating animals deal with the constraints they face when sequentially sampling the world through sound by adjusting acoustic information flow from slow to extremely fast in a highly dynamic manner. Our results further highlight the paramount importance of high behavioural flexibility for acquiring information.

Hand-Foot Coupling: An Advantage for Crossed Legs

It is difficult to perform distinct, simultaneous motor actions with the ipsilateral hand and foot; for example, clockwise circles with the right hand and counter-clockwise circles with the right foot. By chance, we discovered that this hand-foot coupling task is easier when seated with legs crossed. We consider various explanations. First, that there are reduced demands on the contralateral hemisphere when the motor programme of the right foot is executed on the left side of the body. Second, that the legs-crossed scenario is easier because movements are symmetrical with respect to body midline. By considering related motor actions, we conclude that neither of these explanations provides a full account. Thus, we suggest a third explanation, which is that coupling effects are reduced by virtue of increased postural stability and reduced anticipatory postural adjustments.

How does simulation of an observed external body state influence categorisation of an easily graspable object?

Several works have provided evidence of a resonant motor effect while observing a hand interacting with painful stimuli. The aim of this work is to show that participants are sensitive to the observation of an injured hand when they have to categorise an easily graspable object with their own hand. In Experiment 1, participants indicated whether or not photographs of objects (graspable or non-graspable, left or right oriented) could be grasped with their dominant hand, by tapping a key on a keyboard. Target objects were preceded by primes consisting of photographs of hands (injured vs healthy) in a grasping posture (power grasp). Experiment 2 consisted of two phases: In the first phase, participants had to categorise square or circle shapes. After their response (Group 1: tapping a key vs Group 2: constricting a hand grip), photograph of two types of hand (injured vs healthy) was displayed on the computer screen. In the second phase, participants had to indicate whether objects could be easily grasped with their dominant hand. Target objects were preceded by primes (square and circle) as shown in the first phase. Results show that response times were slower when the graspable target objects were right oriented and preceded by the photograph or a geometric shape associated with an injured hand. This response delay was accentuated in the handgrip condition. These results highlight that the view of an injured hand activates motor programme and pain mechanisms associated with participants relative to the consequences of the simulated grasping action.

Whisking and whisker kinematics during a texture classification task

Rats explore objects by rhythmically whisking with their vibrissae. The goal of the present study is to learn more about the motor output used by rats to acquire texture information as well as the whisker motion evoked by texture contact. We trained four rats to discriminate between different grooved textures and used high-speed video to characterize whisker motion during the task. The variance in whisking parameters among subjects was notable. After whisker trimming, the animals changed their behaviour in ways that appear consistent with an optimization of whisker movement to compensate for lost information. These results lead to the intriguing notion that the rats use an information-seeking ‘cognitive’ motor strategy, instead of a rigid motor programme. Distinct stick/slip events occurred during texture palpation and their frequency increased in relation to the spatial frequency of the grooves. The results allow a preliminary assessment of three candidate texture-coding mechanisms—the number of grooves encountered during each touch, the temporal difference between groove contacts and the spatial pattern of groove contacts across the whiskers.