Ramamoorthy Rajkumar

A 100-Channel 1-mW Implantable Neural Recording IC

This paper presents a fully implantable 100-channel neural interface IC for neural activity monitoring. It contains 100-channel analog recording front-ends, 10 multiplexing successive approximation register ADCs, digital control modules and power management circuits. A dual sample-and-hold architecture is proposed, which extends the sampling time of the ADC and reduces the average power per channel by more than 50% compared to the conventional multiplexing neural recording system. A neural amplifier (NA) with current-reuse technique and weak inversion operation is demonstrated, consuming 800 nA under 1-V supply while achieving an input-referred noise of 4.0 μVrms in a 8-kHz bandwidth and a NEF of 1.9 for the whole analog recording chain. The measured frequency response of the analog front-end has a high-pass cutoff frequency from sub-1 Hz to 248 Hz and a low-pass cutoff frequency from 432 Hz to 5.1 kHz, which can be configured to record neural spikes and local field potentials simultaneously or separately. The whole system was fabricated in a 0.18-μm standard CMOS process and operates under 1 V for analog blocks and ADC, and 1.8 V for digital modules. The number of active recording channels is programmable and the digital output data rate changes accordingly, leading to high system power efficiency. The overall 100-channel interface IC consumes 1.16-mW total power, making it the optimum solution for multi-channel neural recording systems.

Specific Inhibition of p25/Cdk5 Activity by the Cdk5 Inhibitory Peptide Reduces Neurodegeneration In Vivo

The aberrant hyperactivation of Cyclin-dependent kinase 5 (Cdk5), by the production of its truncated activator p25, results in the formation of hyperphosphorylated tau, neuroinflammation, amyloid deposition, and neuronal death in vitro and in vivo. Mechanistically, this occurs as a result of a neurotoxic insult that invokes the intracellular elevation of calcium to activate calpain, which cleaves the Cdk5 activator p35 into p25. It has been shown previously that the p25 transgenic mouse as a model to investigate the mechanistic implications of p25 production in the brain, which recapitulates deregulated Cdk5-mediated neuropathological changes, such as hyperphosphorylated tau and neuronal death. To date, strategies to inhibit Cdk5 activity have not been successful in targeting selectively aberrant activity without affecting normal Cdk5 activity. Here we show that the selective inhibition of p25/Cdk5 hyperactivation in vivo, through overexpression of the Cdk5 inhibitory peptide (CIP), rescues against the neurodegenerative pathologies caused by p25/Cdk5 hyperactivation without affecting normal neurodevelopment afforded by normal p35/Cdk5 activity. Tau and amyloid pathologies as well as neuroinflammation are significantly reduced in the CIP–p25 tetra transgenic mice, whereas brain atrophy and subsequent cognitive decline are reversed in these mice. The findings reported here represent an important breakthrough in elucidating approaches to selectively inhibit the p25/Cdk5 hyperactivation as a potential therapeutic target to reduce neurodegeneration.

A 0.45 V 100-Channel Neural-Recording IC With Sub-

Neural prosthetics and personal healthcare have increasing need of high channel density low noise low power neural sensor interfaces. The input referred noise and quantization resolution are two essential factors which prevent conventional neural sensor interfaces from simultaneously achieving a good noise efficiency factor and low power consumption. In this paper, a neural recording architecture with dynamic range folding and current reuse techniques is proposed and dedicated to solving the noise and dynamic range trade-off under low voltage low power operation. Measured results from the silicon prototype show that the proposed design achieves 3.2 μVrms input referred noise and 8.27 effective number of bits at only 0.45 V supply and 0.94 μW/channel power consumption.

\mu {\rm W}

Adaptation of the nervous system to different chemical and physiologic conditions is important for the homeostasis of brain processes and for learning and remembering appropriate responses to challenges. Although processes such as tolerance and dependence to various drugs of abuse have been known for a long time, it was recently discovered that even a single pharmacologically relevant dose of various drugs of abuse induces neuroplasticity in selected neuronal populations, such as the dopamine neurons of the ventral tegmental area, which persist long after the drug has been excreted. Prolonged (self-) administration of drugs induces gene expression, neurochemical, neurophysiological, and structural changes in many brain cell populations. These region-specific changes correlate with addiction, drug intake, and conditioned drugs effects, such as cue- or stress-induced reinstatement of drug seeking. In rodents, adolescent drug exposure often causes significantly more behavioral changes later in adulthood than a corresponding exposure in adults. Clinically the most impairing and devastating effects on the brain are produced by alcohol during fetal development. In adult recreational drug users or in medicated patients, it has been difficult to find persistent functional or behavioral changes, suggesting that heavy exposure to drugs of abuse is needed for neurotoxicity and for persistent emotional and cognitive alterations. This review describes recent advances in this important area of research, which harbors the aim of translating this knowledge to better treatments for addictions and related neuropsychiatric illnesses.

/Channel Consumption in 0.18

The medial prefrontal cortex (mPFC) in the rat has been implicated in a variety of cognitive processes, including working memory and expression of fear memory. We investigated the inputs from a brain stem nucleus, the nucleus incertus (NI), to the prelimbic area of the mPFC. This nucleus strongly expresses corticotropin‐releasing factor type 1 (CRF1) receptors and responds to stress. A retrograde tracer was used to verify connections from the NI to the mPFC. Retrogradely labelled cells in the NI expressed CRF receptors. Electrophysiological manipulation of the NI revealed that stimulation of the NI inhibited spontaneous neuronal firing in the mPFC. Similarly, CRF infusion into the NI, in order to mimic a stressful condition, inhibited neuronal firing and burst firing in the mPFC. The effect of concurrent high‐frequency stimulation of the NI on plasticity in the hippocampo‐prelimbic medial prefrontal cortical (HP‐mPFC) pathway was studied. It was found that electrical stimulation of the NI impaired long‐term potentiation in the HP‐mPFC pathway. Furthermore, CRF infusion into the NI produced similar results. These findings might account for some of the extra‐pituitary functions of CRF and indicate that the NI may play a role in stress‐driven modulation of working memory and possibly other cognitive processes subserved by the mPFC.

\mu{\rm m}

Conventional neural-recording systems face limitations in simultaneously achieving a good NEF and low power consumption [1-4]. This is because the input amplifier current consumption is dictated by an input-referred noise requirement that determines the system sensitivity, while the supply voltage is determined by a DR requirement at the analog recording chain output that limits the maximum achievable resolution of the A-to-D conversion. In this paper, a power-efficient neural-recording architecture using a DR-folding technique is presented to enable low-voltage operation without compromising the DR performance. The proposed architecture can operate with only half of the typically required supply voltage, which results in about 50% power reduction.

CMOS

The nucleus incertus (NI), a brainstem nucleus found in the pontine periventricular grey, is the primary source of the neuropeptide relaxin-3 in the mammalian brain. The NI neurons have also been previously reported to express several receptors and neurotransmitters, including corticotropin releasing hormone receptor 1 (CRF₁) and gamma-aminobutyric acid (GABA). The NI projects widely to putative neural correlates of stress, anxiety, depression, feeding behaviour, arousal and cognition leading to speculation that it might be involved in several neuropsychiatric conditions. On the premise that relaxin-3 expressing neurons in the NI predominantly co-express CRF₁ receptors, a novel method for selective ablation of the rat brain NI neurons using corticotropin releasing factor (CRF)-saporin conjugate is described. In addition to a behavioural deficit in the fear conditioning paradigm, reverse transcriptase polymerase chain reaction (RT-PCR), western blotting (WB) and immunofluorescence labelling (IF) techniques were used to confirm the NI lesion. We observed a selective and significant loss of CRF₁ expressing cells, together with a consistent decrease in relaxin-3 and GAD65 expression. The significant ablation of relaxin-3 positive neurons of the NI achieved by this lesioning approach is a promising model to explore the neuropsychopharmacological implications of NI/relaxin-3 in behavioural neuroscience.

Mechanisms of Action and Persistent Neuroplasticity by Drugs of Abuse

A number of atypical antipsychotic drugs are known to perturb appetite regulation causing greater hyperphagia in humans and rodents than earlier generation typical agents. However, the neuronal structures that underlie hyperphagic effects are poorly understood. Arcuate nucleus (ArcN), paraventricular hypothalamic nucleus (PVN), paraventricular thalamic nucleus (PVA) and nucleus incertus (NI) have been implicated in appetite regulation. The NI is the principal source of the relaxin-3 (RLN3) peptide, which is reported to have orexigenic effects. Moreover, ArcN, PVN, and PVA receive RLN3 immunoreactive fibers from the NI and express relaxin family peptide type 3 (RXFP3) receptor. The present study was designed to evaluate the acute effects of clozapine (atypical), chlorpromazine (typical) and fluphenazine (typical) on c-Fos expression (a marker of neuronal response) in these appetite-related centers of the rat brain. The numbers of c-Fos expressing neurons in these structures were counted in immunofluorescence stained brain sections. Acute treatment with clozapine, chlorpromazine and fluphenazine differentially influenced c-Fos expression in these brain structures. This study is also the first demonstration that antipsychotics influence the NI. The patterns of the effects of these antipsychotics are related to their reported hyperphagic properties.

Corticotropin-releasing factor infusion into nucleus incertus suppresses medial prefrontal cortical activity and hippocampo-medial prefrontal cortical long-term potentiation.

Relaxin‐3 has been proposed to modulate emotional–behavioural functions such as arousal and behavioural activation, appetite regulation, stress responses, anxiety, memory, sleep and circadian rhythm. The nucleus incertus (NI), in the midline tegmentum close to the fourth ventricle, projects widely throughout the brain and is the primary site of relaxin‐3 neurons. Over recent years, a number of preclinical studies have explored the function of the NI and relaxin‐3 signalling, including reports of mRNA or peptide expression changes in the NI in response to behavioural or pharmacological manipulations, effects of lesions or electrical or pharmacological manipulations of the NI, effects of central microinfusions of relaxin‐3 or related agonist or antagonist ligands on physiology and behaviour, and the impact of relaxin‐3 gene deletion or knockdown. Although these individual studies reveal facets of the likely functional relevance of the NI and relaxin‐3 systems for human physiology and behaviour, the differences observed in responses between species (e.g. rat vs. mouse), the clearly identified heterogeneity of NI neurons and procedural differences between laboratories are some of the factors that have prevented a precise understanding of their function. This review aims to draw attention to the current preclinical evidence available that suggests the relevance of the NI/relaxin‐3 system to the pathology and/or symptoms of certain neuropsychiatric disorders and to provide cognizant directions for future research to effectively and efficiently uncover its therapeutic potential.

A 0.45V 100-channel neural-recording IC with sub-µW/channel consumption in 0.18µm CMOS

For real-time monitoring of brain activities, a highdata-rate, low-power, and highly mobile neural recording system is desirable. This paper presents a complete chipset for a 100-channel wireless neural recording system, which consists of 3 ICs - a neural interface (NI) IC and a wireless power RX and data TX IC for an implant unit (IU), and a wireless data RX IC for an external head unit (EHU). With a dual S/H NI architecture and a burst-mode (BM) wideband (WB) FSK TX, the IU achieves a 100-channel recording and wireless transmission at 54.24Mb/s while consuming only 6.6mW. Using power coupling with optimal resonant load transformation and high-efficiency rectifier and LDO circuits, the whole wireless power link achieves 40% efficiency over 1cm distance with 0.5cm tissue in between. The EHU needs to transmit the RF power lower than 30mW to operate the IU. The EHU is implemented using a crystal-less BM WB FSK RX consuming only 14.4mW at 27.12Mb/s.